When the victim of an event is blamed, or partially blamed, for their own attack. Mainly used in context with rape, domestic abuse, sexual harassment and sexual assault, but can be applied to other situations. It wrongly shifts blame from the guilty party onto the victim, and therefore doesn't (or makes it more difficult to) punish the one truly at fault. The term was popularized by the SlutWalk movement, which started after a Canadian police officer advised female students to "avoid dressing like sluts" in order to avoid being victimized.
Person#1: "I know being raped is bad and all, but she was flirting with him the whole night, and wearing that low-cut shirt. What'd she expect?"
Person#2: "Dude, sex has NOTHING to do with rape. It's all about power. And even if it did, flirting and wearing a low-cut top doesn't mean she was asking to be attacked like that. So, why don't you quit the victim shaming and admit what that guy did was wrong."