The following information is available on the Consumer Financial Protection Bureau website: Health Savings Accounts (HSAs) and Flexible Spending Accounts (FSAs) allow you to set aside pre-tax money, sometimes directly from your paycheck, to pay for eligible health/medical expenses. Your employer may offer an FSA or an HSA as a separate account to pay for eligible medical expenses. The accounts may be linked to a card.
More information can be found here: https://www.consumerfinance.gov/ask-cfpb/what-is-a-flexible-spending-account-fsa-card-health-savings-account-card-hsa-en-417/.