Flexible spending account
In the United States, a flexible spending account (FSA), also known as a flexible spending arrangement, is a type of tax-advantaged financial account first established in 1978. One significant disadvantage to using an FSA is that remaining funds in excess of a specified amount that are not used by the end of the plan year are forfeited to the employer, known as the "use it or lose it" rule.
Source: Wikipedia — Flexible spending account (CC BY-SA 4.0)