1. In the social hierarchy of an animal group, a male occupying a position secondary to the dominant "alpha male." Emerging research on animal groups suggests that beta males may have more complex roles than previously thought.

2. By extension, a man comfortable with engaging in non-stereotypical male behaviors and having personality traits that contrast with the stereotypically dominant and aggressive "alpha male." In this usage, the term is used positively or affectionately. I really like that David is so chill. He's a real beta male, and I'm into it.

3. A derisive term for a man regarded as passive or weak (in contrast to the "alpha male"). I can't believe Mike lets his girlfriend tell him what to do—what a beta male.