This is complicated. According to the fems on DU, a white-knight is a derogatory term used by anti-fem men for men that support the fems' point of view.
From what I can decipher, the anti-fem men don't really use that term, but it's implied, according to the fems.
Yeah, I know...... 
white knight, mangina, beta, and omega are types of males commonly described in the manosphere. The other three are variants of betas.
A beta is a typcal nice guy. He listens to the girl talk about her day, bitch about her friends, complain about life, while being gentle and supportive, perhaps buying her things to show her he has money. All in an effort to get laid while ignoring that his behavior is ultimately undoing any real chance of that.
A white knight will defend the behavior of women, even if said behavior is indefensible, he may say it is in the spirit of equality, but it isn't honest. Some of Will Pitt's screeds paint him as a white knight.
Manginas are a lot like white knights except that instead of "valiantly defending the right of a woman to behave like a drunken sailor" they commiserate with women and talk about how unfair it is and how somebody needs to do something to make it so men can "feel women's pain".
An omega falls into two categories. Type 1 is a mess, He is utterly unable to hold a conversation with a normal woman. Type 2 is potentially dangerous, since he can't live within societal rules he may try to make his own rules and decide to take what he wants. Fortunately, omegas are a very small percent of the population.
I have been around the manosphere lately, maybe licking my wounds, maybe trying to learn some things. I have encountered those terms quite a bit lately.
