Sedevacantism

Okay kiddo, so have you ever heard of the Pope? He's the leader of the Catholic Church and is considered very important by Catholics. Well, some people who used to be in the Catholic Church but aren't anymore think that the Pope and all the other leaders of the Church since the 1960s aren't really popes at all! They say that these popes and leaders have said and done things that go against what the Church has always believed, and so they don't count as real popes.

These people are called sedevacantists, which is a fancy word that means "empty seat". That's because they believe that the position of the Pope is currently empty since they don't recognize the current or recent popes as real ones. This means they don't follow any of the rules or teachings of the current Catholic Church, since they don't think it's really the true Church.

To sum it up, sedevacantists are people who don't think the current Catholic Church leaders are real Popes, and so they don't follow them or consider them part of the true Church.