Tic

A tic is each time unit in-game. By default 1 second equals 30 tics.

From the EDuke32 source code:

// this used to be TICRATE/GAMETICSPERSEC, which was 120/26 = 4.615~ truncated to 4 by integer division
#define TICSPERFRAME        4
#define TICRATE             120

Because the word "tic" can mean a variety of other timing units, the less ambigious "game tic" should be preferred.