Key Takeaways
- Parts A–D are labels for hospital insurance (A), medical insurance (B), Medicare Advantage (C), and drug coverage (D)—not four separate bills for everyone.
- Plan paperwork uses words like formulary, benefit period, and MOOP to explain what is covered, what you owe, and when rules apply.
- Original Medicare and Medicare Advantage follow different billing and network rules; the right fit depends on your doctors, drugs, and budget.
- Always verify definitions that affect money or enrollment on Medicare.gov and your plan’s official documents for your ZIP code and plan year.
- How to Use This Glossary
- Original Medicare vs Medicare Advantage in One Sentence Each
- Part A Terms Worth Knowing
- Part B Terms Worth Knowing
- Part C Terms Worth Knowing
- Part D and Prescription Terms Worth Knowing
- Terms Dual-Eligible Readers Often Hear in New York
- Enrollment and Timing Terms
- Frequently Asked Questions
- Take the Next Step
This article gives plain-English definitions for words you will see in mailings, plan summaries, and doctor bills. It is not legal, tax, or medical advice, and it cannot replace your plan’s Evidence of Coverage or the official Medicare handbook.
If a term affects premiums, penalties, or eligibility, treat this page as a map—not the final word. Use Get started with Medicare for program basics, your Summary of Benefits for plan rules, and Medicare Plan Compare for options in your county. For dollar amounts that change each year (like the Part B deductible), our companion post walks through 2026 figures with CMS links: Medicare Parts A–D costs in 2026.
Networks, drug lists, and Medicaid coordination can look different in New York than in other states—even when the Medicare side follows national rules. When a word touches Medicaid, long-term care, or a Special Needs Plan, read slowly and confirm details with official New York resources and your plan.
Original Medicare is Part A and Part B run by the federal Medicare program. Medicare Advantage is Part C: a Medicare-approved private plan that bundles Part A and Part B (and usually Part D) into one package with its own rules.
Part A helps cover inpatient hospital stays, limited skilled nursing after a hospital stay, hospice, and some home health in defined situations. Part B helps cover outpatient care, doctor visits, many preventive services, durable medical equipment, and more. Many people use Part D (drug coverage) alongside Original Medicare, or choose Part C instead.
Part C plans must cover everything Original Medicare covers, but they can use managed care tools like networks, copays, and prior authorization for certain services—within Medicare rules. Benefits beyond Original Medicare (like dental or fitness programs) vary by plan and service area. Start with our Medicare Advantage overview if you are comparing big-picture options.
Part D helps cover outpatient prescription drugs. You can get it through a standalone Part D plan with Original Medicare (often paired with a supplement) or bundled in many Medicare Advantage plans. Formularies and cost tiers still vary by plan.
Part A is often called hospital insurance, but the name can mislead people: not every “hospital visit” is covered the same way, and not every service at a hospital is Part A.
Inpatient means a doctor formally admitted you to the hospital as an inpatient. Observation status can happen in a hospital bed but still be billed as outpatient under Part B rules in many cases—which can change what you owe and whether a follow-up skilled nursing stay is covered. If you are unsure, ask the hospital team whether you are an inpatient or under observation, and follow up with Medicare’s materials on hospital stays.
A benefit period is not the same as a calendar year. For Part A inpatient hospital coverage, it begins the day you are admitted as an inpatient and ends when you have been out of the hospital or skilled nursing facility for 60 days in a row. You can have more than one benefit period in a year, which matters for the Part A deductible rules summarized on Medicare.gov — Costs.
Skilled nursing care is short-term, medically necessary care—like certain nursing and therapy services—not long-term custodial care. Medicare coverage in a SNF typically requires a qualifying hospital stay and meeting other conditions. Long-term care in a nursing home is a different conversation; do not assume Part A pays for extended stays.
Most people get premium-free Part A if they or a spouse paid Medicare taxes long enough while working (often described as 40 quarters of work). If you are not premium-free, you may be able to buy Part A; see Medicare.gov — Costs for current buy-in amounts and rules.
Part B is medical insurance for outpatient care and many doctor services. Cost-sharing words show up on almost every bill.
- Premium: the fixed amount you pay to keep Part B (usually monthly).
- Deductible: the amount you pay each year before Medicare pays its share for many Part B services.
- Coinsurance: your share after the deductible—often 20% of the Medicare-approved amount for many Part B services when the provider accepts assignment.
Exact Part B premiums and deductibles change over time; CMS publishes them annually. For 2026 numbers, use Medicare.gov — Costs or the CMS fact sheet linked from our Parts A–D costs guide.
When a doctor or supplier accepts assignment, they accept the Medicare-approved amount as full payment for covered services (except your share). If a provider does not accept assignment, you might owe up to an additional limiting charge above the Medicare-approved amount in some situations. This is one reason bills feel “random” even with the same diagnosis.
Preventive services (like certain screenings) are often covered at no cost to you when you use an eligible provider and meet Medicare rules. If a visit turns into diagnostic testing or treatment, different cost-sharing may apply. This distinction is billing-related, not moral—ask the office how Medicare will bill the visit if you are confused.
IRMAA (Income-Related Monthly Adjustment Amount) is an extra charge on Part B and Part D premiums for people with higher reported incomes, based on tax information Medicare uses from the IRS. If your income drops because of retirement, marriage changes, or certain life events, you may be able to request a reconsideration through Social Security’s process. Medicare summarizes IRMAA on its costs page; this article does not list every bracket because they can change.
Part C plans are sold by private companies but must follow Medicare laws. The vocabulary below explains how your plan controls access and spending.
- HMO (Health Maintenance Organization): you usually choose a primary care doctor and need referrals for many specialists; care outside the network may not be covered except in emergencies.
- PPO (Preferred Provider Organization): you typically have more freedom to see out-of-network providers, but you usually pay less in-network.
Neither label automatically means “better”—it depends on whether your doctors participate and how you like to manage care.
MOOP stands for maximum out-of-pocket. Medicare Advantage plans must limit how much you pay in a year for covered Part A and Part B services—after you hit the limit, you pay $0 for covered services for the rest of the year. What counts toward MOOP, what is excluded, and the dollar limit vary by plan and can change each year—check your Evidence of Coverage.
- Prior authorization: your plan may require approval before it covers certain tests, procedures, or drugs.
- Referral: a process where your primary care clinician sends you to a specialist (common in HMOs).
- Network: the doctors, hospitals, and pharmacies that contract with your plan.
- Out-of-network: care outside that contract—sometimes not covered (except emergencies), sometimes covered at a higher cost share.
Many Medicare Advantage plans offer additional benefits Original Medicare does not include as standard—like limited dental, vision, or hearing. Benefits are not standardized the same way nationwide; read the fine print for annual caps, networks, and copays.
Need help translating your plan’s vocabulary into real choices? Call SJM Cares at (347) 696-6757 for a free, no-obligation conversation with a licensed Medicare advisor in Brooklyn.
A formulary is your plan’s list of covered drugs. Tiers are groups that usually have different copays or coinsurance (for example, generic vs brand). A preferred pharmacy is a network pharmacy where you may pay less than at a standard in-network pharmacy, depending on plan design.
Most Part D plans have stages: deductible (if your plan has one), initial coverage, coverage gap, then catastrophic coverage. The coverage gap is not a literal hole in care—it is a phase where you may pay more out of pocket until you reach a total out-of-pocket threshold that Medicare defines using True Out-of-Pocket (TrOOP) rules. Exact percentages and thresholds can change by year; read Medicare’s official explanation of the Part D coverage gap for the current rules.
TrOOP is the running total of certain out-of-pocket drug costs that Medicare uses to move you through Part D payment stages. Not every dollar you spend counts the same way. Use your plan’s statements and Medicare’s consumer pages rather than guessing from social media posts.
Medicare is federal health insurance mainly for people 65+ and some younger people with disabilities. Medicaid is a state-administered program for people with limited income and resources, with rules that vary by state.
Someone who is dual eligible has both Medicare and Medicaid (full or partial assistance depending on the program). A Dual Eligible Special Needs Plan (D-SNP) is a type of Medicare Advantage plan designed to coordinate benefits for people who meet eligibility rules. Details depend on your Medicaid level and the plan—start with our D-SNP overview and confirm eligibility with official program counselors.
These acronyms describe windows, not optional “tips.” Missing certain windows can lead to late enrollment penalties for Part B (and sometimes Part A) depending on your situation.
- IEP (Initial Enrollment Period): the seven-month window around turning 65 (or your Medicare start date for disability) when many people first enroll.
- AEP (Annual Election Period): October 15–December 7 each year for most people to change Medicare Advantage and Part D coverage for the next year.
- OEP (Medicare Advantage Open Enrollment Period): January 1–March 31 for people who already have Medicare Advantage to make a limited set of changes.
- SEP (Special Enrollment Period): a personal enrollment window triggered by specific events (like moving or losing other coverage), with rules that vary by event.
For dates, examples, and NYC-friendly context, read AEP, OEP, and SEP for Medicare in NYC. For the authoritative program rules, use Medicare’s enrollment pages.
A premium is what you pay to have coverage (often monthly). A deductible is what you pay first for covered services before your plan or Medicare starts paying its share—until the deductible is met, if your plan has one. Many people pay a Part B premium even if they rarely see a doctor.
It is the payment amount Medicare establishes as reasonable for a covered service. If your provider accepts assignment, your coinsurance is usually based on that approved amount—not on a higher “chargemaster” price a facility might list.
No. Medigap (Medicare Supplement Insurance) works with Original Medicare to help pay certain out-of-pocket costs like coinsurance. Part C (Medicare Advantage) is an alternative way to get Part A and Part B benefits through a private plan. You generally cannot use a Medigap policy to pay Medicare Advantage copays.
A formulary is your Part D plan’s covered drug list. Plans can change formularies during the year within Medicare rules—often with advance notice for certain changes. If you take maintenance medications, review updates from your plan, especially during renewal season.
MOOP limits your yearly spending on covered Part A and Part B services in Medicare Advantage. It does not necessarily cap everything you spend on healthcare (for example, certain services, premiums, or Part D spending may be tracked separately). Read your plan’s MOOP section carefully.
Many people still enroll in creditable drug coverage to avoid a late enrollment penalty if they later need Part D. If you have other drug coverage (like from an employer plan), get proof that it is creditable. Medicare explains the penalty concept on its Part D late enrollment penalty page.
If Medicare’s vocabulary feels like a second language, you are not alone—especially during plan changes and life transitions. SJM Cares helps Brooklyn and NYC residents compare Medicare Advantage and D-SNP options available in their area, using plan documents—not slogans.
Call us at (347) 696-6757 or schedule an appointment online.
Written by Hamad Amir, licensed insurance agent and founder of SJM Insurance Services, LLC. Licensed in New York and New Jersey (License #LB-1024797). Specializing in Medicare Advantage and D-SNP plans for Brooklyn and NYC residents.
Image credit: Hero photo from Unsplash (Unsplash License—free commercial use).
Disclaimer: This article is for educational and informational purposes only and does not constitute professional insurance, financial, or legal advice. For personalized guidance, call a licensed SJM Cares advisor at 917-373-0117.
We do not offer every plan available in your area. Currently we represent 10 organizations which offer Medicare Advantage HMO, PPO, PFFS, and PDP plans in your area. Please contact Medicare.gov, 1-800-MEDICARE (TTY: 1-877-486-2048), or your local State Health Insurance Assistance Program (SHIP) to get information on all of your options.
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