A protest is a formal declaration of objection. If students at your school are fed up with the overly restrictive dress code, they might stage a protest. Washington, D.C. is often the site of political protests.
Protest is both a noun and a verb. You've probably seen news about protests, because people all over the world organize them when they need to get a message across urgently. A protest doesn't have to be on the world scale, however. You might protest against eating frozen pizza for the third night in a row, and you've certainly seen a little kid protest against going to bed. When protest is political, it's also known as dissent.