Quid Pro Quo is Latin and stand for the proposition of "this for that." In the context of sexual harassment it refers to a situation where the boss tell you to have sex in return for favorable employment consideration. So if you have sex with the boss something good work related will happen to you. Of course this creates a hostile work environment for everyone else at work. If this happens to you at work, there are things you can do to protect yourself.
First, you should contact an employment attorney who concentrates in sexual harassment cases. Second, you should try and save any text messages or emails. If you do come forward the burden is on you to prove this actually happened. The boss doesn't have to disprove the allegations against him. You have to prove the allegations against the boss, so keep that in mind.