What is "milstar"

Milstar, originally meaning Military Strategic and Tactical Relay, is a constellation of military communications satellites in geostationary orbit, which are operated by the United States Air Force, and provide secure and jam-resistant worldwide communications to meet the requirements of the Armed Forces of the United States. Six spacecraft were launched between 1994 and 2003, of which five are operational; the third launch failed, both damaging the satellite and leaving it in an unusable orbit.