The TSP is a retirement savings plan for civilians who are employed by the United States Government and members of the uniformed services. The Federal Retirement Thrift Investment, administers the Thrift Savings Plan (TSP). The Ballpark Savings E$timate will accept a dollar amount up to the tax deferral limit of $19,500, or, a percentage of your wages for your TSP contribution (but that percentage cannot be more than the IRS's allowable maximum of $19,500).
For more information on the TSP, see the TSP website at: www.tsp.gov