A Gamma Male is the third step down in the hierarchical taxonomy of the male sex, directly below a Beta Male and fathoms below an Alpha male. A Gamma Male unconsciously adopts or duplicates female behaviors, values, or expectations in the hopes of winning female admiration. He does this because he is too paralyzingly timid to attempt to directly win the affections of female through the Alpha Male traits of confidence and swagger.
The Gamma Male never appears confident or comfortable with whom he is. In a relationship with a female, he acts like one of her girlfriends. Further, the Gamma Male is wont to show his "feelings" in a cringe worthy manner, bringing audible sighs of shock and disgust from even the most unassertive and passive Beta Males. In comparison to other males of higher evolutionary development, he is a pitiful creature.
You know that screaming queen on 'The Bachelorette' who went and got a tattoo of a heart and a shield on his wrist to profess his undying devotion to the girl he had only known for a few weeks? Yeah, total Gamma Male.