The term 'Tennis Call' is a term used to describe the act of calling out the score in a tennis match. It is the responsibility of the players or the umpire to call out the score after each point is played. The three letters LET stand for 'Loud, Echoed, and Timed'. This means that the call should be loud enough for all players to hear, echoed back by the other player, and timed correctly so that the score is accurately recorded.