A chess repertoire is the set of openings and variations a player chooses to study and play consistently — one system for White and one or more responses for each of Black’s main replies — so that every game starts from familiar, well-understood positions.
Building a repertoire means selecting specific answers to the opponent’s most common moves. For example, a player might choose 1.e4 as White, answer 1.e4 with the Sicilian Defence as Black, and meet 1.d4 with the King's Indian Defence. These consistent choices reduce the total amount of theory to learn while still producing rich, playable positions.
In practice, a narrow and well-understood repertoire beats a broad but shallow one every time. For players between 800 and 1400 ELO, the priority is grasping the typical ideas and plans behind each line rather than memorising long move sequences. A solid repertoire means entering positions you have seen before — and that accumulated familiarity is a genuine competitive edge.