Plain-language terms
Medicare glossary
Plain-language definitions of the Medicare terms you'll run into most — from Parts A, B, and D to IRMAA, deductibles, coinsurance, formularies, and the enrollment periods.
Medicare comes with a lot of jargon. Here are plain-language definitions of the terms you’ll run into most, each with a short explainer and links to learn more.
Original MedicareParts A and B, run directly by the federal government.
Part AMedicare's hospital insurance.
Part BMedicare's medical insurance.
Part DMedicare's prescription drug coverage.
Medicare Advantage (Part C)All-in-one private-plan alternative to Original Medicare.
Medicare Supplement (Medigap)Policy that covers Original Medicare's out-of-pocket costs.
Special Needs Plan (SNP)An Advantage plan built for a specific condition or situation.
PremiumThe monthly amount you pay to keep coverage.
DeductibleWhat you pay before coverage starts paying.
CoinsuranceYour percentage share of a cost after the deductible.
CopaymentA fixed dollar amount for a covered service or drug.
Out-of-pocket maximumThe yearly cap on what you pay for covered care.
Coverage gap (donut hole)The old Part D gap, replaced by a $2,100 cap in 2026.
IRMAAIncome-related surcharge on Part B and Part D premiums.
MAGIModified adjusted gross income, used to set IRMAA.
FormularyA drug plan's list of covered medications.
Prior authorizationA plan's required approval before certain care or drugs.
Creditable coverageDrug coverage as good as Part D, which prevents a penalty.
Initial Enrollment PeriodYour first window to sign up for Medicare.
Annual Enrollment PeriodThe fall window to change Medicare coverage.
Special Enrollment PeriodA window to change coverage after a qualifying life event.
Guaranteed issueYour right to buy certain Medigap plans without health questions.
Late enrollment penaltyA permanent premium add-on for enrolling late without coverage.
Extra HelpA federal program that lowers Part D drug costs for lower incomes.
Medicare Savings ProgramsState programs that help pay Medicare premiums and cost-sharing.
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