Bear is a sub-cultural micro-label used by gay men who express themselves as what is typically seen as masculine and defy the stereotypes typically applied to gay men, such as getting pedicures and femininity. For example a bear may enjoy drinking beer, hunting, watching football or having thick beards.
The bear subculture was created to celebrate such masculine traits, and unite each other, similar to how femme lesbians defy the stereotype of being masculine.
The bear subculture is not to be confused with furries, and masculine gay men are known as bears because they are hairy and depicted as tough.