It's a form of direct protest in which a group want to encourage social or political change. Groups often refuse to move from the place in which they are protesting until they see a significant change. SNCC, for example, organised many restaurant counter sit-ins in the 1960s. This was to protest against racial segregation and discrimination. Many people reacted negatively to the sit-ins movement during this time, but the majority of protesters continued to use peaceful protest methods so that they didn't sacrifice their morals and could attract media attention.
