It means simply "Loud and Clear", I received your broadcast. Used mostly over the radio as a response to "Radio check, over"
U.S.M.C. - "Checkmate One to White Rook, radio check, over" response "White Rook to Checkmate One, Gotcha Lima Charlie."
A millitary term used by the U.S.M.C. Meaning Loud and Clear for two reasons but the most improtant is that it sounds cool and official.