They’re denotations for the spaces between offensive linemen. The typical distance (called a split) is two feet, although that can vary. Gaps are referred to by letters extending out from either side of the center, A through C, or D depending on how many players there are to one side.

In football, gaps refer to the spaces between offensive linemen. These gaps are typically about two feet wide and are designated by letters: These gaps serve as both protection points for the offense and attack points for the defense.