A protest vote is a vote for someone or something that you don't like in order to show your dissatisfaction. It's a way to show that you are not happy with the choices you have been given, especially when those choices are not what you would like them to be. For example, if there is only one candidate running, and you don't like that person, you might choose to vote for someone else as a protest. By doing this, you are making a statement that you would prefer a different option.