An absolute handicap system is an approach to making even games even regardless of player strength. In general it relates to the idea of playing for points, not for the win. For example, if player A is 4 points stronger than player B, they play with 6.5-4 = 2.5 points komi. If B wins often at -4 points, the players will eventually agree on a new handicap, which is the number of points describing their average difference in their strength.
This allows playing competitive even games instead of nine stone games - black just tries to lose by less each time. It is another kind of "real" fair game.
Players of the same strength may also give each other handicap stones. By playing alternate games, the proper komi will become clear.