An HSA is a tax-advantaged personal financial account. It is like a savings account for paying medical, dental, vision, and prescription health care expenses. Contributions to an HSA may be free of income and/or payroll tax.
An HDHP is a health insurance plan with out-of-pocket spending limits determined by the IRS. Unlike other plans, healthcare costs are paid entirely by the consumer until they reach their deductible.
At the same time, you are protected if you have a significant health event during the year. Once you meet the deductible, the plan will pay its coinsurance percentage for covered services, and when you reach the annual out-of-pocket maximum, the plan generally will pay 100% for the remainder of the year.