Karo-Net was a kind of sport played in tournaments.
In 2369, Odo mentioned Karo-Net in a hypothetical situation as to why he had never dated anyone, because of the undesirable consequences of making compromises. He told Quark in his example, "You want to watch a Karo-Net tournament, she wants to listen to music. So you compromise. You listen to music. You like Earth jazz, she prefers Klingon opera, so you compromise. You listen to Klingon opera. So here you were ready to have a nice evening watching the Karo-Net match and you wind up spending an agonizing night listening to Klingon opera..." (DS9: "A Man Alone")