A franchise is typically defined to be at least two works derived from a common intellectual property. Traditionally, the work has a tautological relationship with the property, but this is not a prerequisite. An enduring staple of the franchise model is the concept of the "crossover", which can be defined as "a story in which characters or concepts from two or more discrete texts or series of texts meet". A consequence of a crossover is that an intellectual property may be utilized by more than one franchise. For example, "" belongs to not only the Batman and Superman franchises, but also to the DC Extended Universe, which is a "shared universe". A shared universe is a particular type of crossover where a number of characters from a wide range of fictional works wind up sharing a fictional world. The most successful shared universe in the medium of film is the Marvel Cinematic Universe, a crossover between multiple superhero properties owned by Marvel Comics. The Marvel Cinematic Universe is also the highest-grossing franchise, amassing over $22 billion at the box office.