A medical savings account available to taxpayers who are enrolled in a High Deductible Health Plan. The funds contributed to the account aren’t subject to federal income tax at the time of deposit. Funds must be used to pay for qualified medical expenses. Unlike a Flexible Spending Account (FSA), funds roll over year to year if you don’t spend them.

References

https://www.healthcare.gov/glossary/health-savings-account-HSA/