Free Medicare basics

Glossary

Plain definitions for general education. This page does not evaluate your coverage or recommend a plan.

Content checked September 26, 2026. Check the linked official pages for current rules.

Part A

Hospital Insurance in Original Medicare. Medicare.gov: compare coverage options

Part B

Medical Insurance in Original Medicare. Medicare.gov: compare coverage options

Part C

Medicare Advantage, another way to get Medicare coverage through a Medicare-approved private plan. Medicare.gov: compare coverage options

Part D

Medicare drug coverage, offered by Medicare-approved private plans. Medicare.gov: how drug plans work

Medigap

Supplement insurance that may help with cost sharing in Original Medicare; it does not cover Medicare Advantage plan costs. Medicare.gov: when to buy Medigap

Premium

An amount paid for coverage, usually monthly, even if you do not use covered services. Medicare.gov: Part D costs

Deductible

An amount you pay for covered care or drugs before the plan starts paying under its rules. Medicare.gov: Part D costs

Copayment

A fixed amount you pay for a covered service or drug. Medicare.gov: Part D costs

Coinsurance

A percentage of the cost you pay for a covered service or drug. Medicare.gov: Part D costs

Formulary

A drug plan's list of covered drugs; each plan has its own list. Medicare.gov: how drug plans work

Network

Doctors, hospitals, and other providers a plan contracts with; using providers outside it may cost more or be restricted. Medicare.gov: compare coverage options

Out-of-pocket limit

A Medicare Advantage plan's yearly limit for covered health services under its rules; it varies by plan. Medicare.gov: Medicare costs

Annual Notice of Change

A plan notice describing changes for the next year, including costs and coverage. Medicare.gov: Annual Notice of Change

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