It’s a simple mechanism for making a group decision. Picking a place to eat dinner, a movie to see, or what game to play next? Anyone can make a suggestion, and anyone can veto any suggestion. If you veto a suggestion, you have to make the next suggestion. No one may suggest something already vetoed.
When this rule is in force, people stop vetoing much and decisions about what to do are made quickly. It is very effective, especially against passive aggressive behavior, and it encourages assertive behavior. Try it out next time two or more people need to make a decision together when there are lots of options.