¡°Black Lives Matter¡± has become a mantra for people protesting police violence against African-Americans.

It¡¯s a hash tag, a popular T-shirt slogan and a movement that is loosely organized ¡ª by design.

Black Lives Matter was founded by three women who popularized the slogan during protests over the 2012 killing of Trayvon Martin, an African-American teen who was shot by George Zimmerman, a neighborhood watch volunteer in Sanford, Florida.