The Thrift Savings Plan (TSP) is a retirement savings and investment plan for federal employees and members of the uniformed services. It offers participants a way to save for retirement through payroll deductions, with various investment options, including government securities and stock index funds. Participants can contribute a portion of their salary to the TSP, and many employers provide matching contributions. The plan is designed to help individuals build a secure financial future, with tax advantages that can enhance savings growth over time.