Nonviolence is a form of social change that completely rejects the use of violence to reach an end. Nonviolence is not passive acceptance, but it is a nonviolent opposition. It is used nowadays as a means of social protest. Those who practice nonviolence believe cooperation and consent are necessary for political structures to survive and thrive, no matter the background.
One great example of nonviolence is the work of Gandhi. He successfully lead nonviolent resistance against the British in India, ultimately leading to the country's independence. Martin Luther King used the same concept to win the struggle for civil rights. The current Dalai Lama made clear that nonviolence is the only way progress can be made with China to reach any sort of deal. Nonviolence works.
Although often linked together, nonviolence and pacifism are different, although similar concepts. Pacifism specifically states that it is the rejection of violence on a personal, moral, and religious level, whereas nonviolence is specific towards a socio-political level. Nonviolence is also contextual. Someone could theoretically promote nonviolence in one area while supporting violence in another.