While a prototype is an abstract average of the members of a category, an exemplar is an actual member of a category, pulled from memory.[citation needed] While prototypes are economical—meaning they are more conducive to quick judgments—exemplars are less so. On the other hand, prototypes are less flexible than exemplars: exemplars can account more easily for atypical category members, such as a penguin being part of the "bird" category, because an exemplar does not average out the characteristics of a category like a prototype does. Exemplars can make sense of variable categories—those with less distinguished characteristics—such as "games", much more so than prototypes, which rely on typical characteristics to determine membership.