World unit
From Halopedia, the Halo wiki
World unit, or wu for short, is a unit of measurement for distance used in the Blam engine, in which the majority of first-person shooter instalments in the Halo series were created. Most measures of distance in the games, for instance red reticle range, are specified in world units internally, despite metres being used in player-facing HUD elements such as objective markers. While the conversion rate to metres varies from game to game, world units themselves usually remain consistent between games.
