From the Slutwalk NYC website:
SlutWalk NYC is part of a worldwide grassroots movement challenging rape culture, victim-blaming and slut-shaming, and working to end sexual and domestic violence.
The SlutWalk protest marches began on April 3, 2011, in Toronto, Canada, and became a movement of rallies across the world. Participants protest against explaining or excusing rape by referring to any aspect of a woman's appearance. The rallies began when Constable Michael Sanguinetti, a Toronto Police officer, suggested that to remain safe, "women should avoid dressing like sluts." The protest takes the form of a march, mainly by young women, where some dress in ordinary clothing and others dress provocatively, like "sluts." There are also speaker meetings and workshops. Some objectors have remarked that this approach is an example of women defining their sexuality in male terms.