A focal point: the option people tend to choose when they must coordinate without communicating, because it seems natural or salient to everyone.
In more detail
Thomas Schelling introduced the idea in The Strategy of Conflict (1960) with the example of strangers told to meet in New York City without agreeing a place. Blockchain designs such as SchellingCoin and Kleros use it as an incentive: reward jurors or oracles who vote with the majority, so that telling the truth becomes the option each expects the others to choose.