A protest party is a group of people who come together because they are upset or angry about something and want to try to change it. It's like when you and your friends get mad because your teacher gave you too much homework, and you all decide to talk to the principal about it. A protest party is kind of like that, but for grown-ups and bigger problems.
Sometimes, people feel like the politicians in charge aren't doing a good job or aren't listening to them, so they start their own party to show their disagreement. They might call themselves something like "The Anti-Corruption Party" or "The Save Our Planet Party."
People who join a protest party want to make their voices heard and try to make changes in the way things are done. They might have marches or rallies where they gather together with signs and shout slogans to get attention. They might also try to get people to vote for them in elections so they can try to make changes from within the government.
Overall, a protest party is a way for people to come together and try to make a difference in the world when they feel like things aren't going the way they want them to.