Traits of provision: either providing resources or validation to others, women (and perhaps men). Beta traits display low value to women if they are are put on too strong or too early in meeting- giving without equity. Beta can be used to describe individual behaviors, as well as people who have an overwhelming amount of beta properties (opposed to alpha).
Interchangeable with cuck. Often used along with it.
The term refers to "beta male", which in turn means "not alpha male" - alpha male being a concept from the study of lions and other like animals, meaning the leader of the pack, who tends to enjoy greater sexual success. Like the word "cuck", it's probably intended to have humiliating sexual overtones when used to label men in particular. However, since the most obvious translations of "alpha male" into a human social context would be Presidents, Mayors and CEOs, calling someone a "beta male" arguably just means "you're a male human being who isn't a President, a mayor or a CEO... at least, at the present time". Perhaps not quite what they had intended.