1. A line drawn horizontally from a point on a billiard table's rail to the corresponding point on the opposite rail, thus defining a region (a balk). In the eponymous balklinebilliards there are four balklines, drawn parallel to and 14 or 18 inches from the cushions of the table, dividing it into nine compartments or divisions, of which the outside eight are the balks. in which only a set number of caroms may be scored before at least one ball must leave the area. Not to be confused with baulk line, though the concepts and etymologies are related. See balk, second definition.
2. Formerly, in "the champions' game", a line drawn diagonally from a long to a short rail at the corners of the table, defining a triangular balk space at each.
3. A type of carombilliardsgame, called balklinebilliards, created to eliminate very high runs in straight-rail that relied on repetitive nurse shots.