Possibilianism is a kind of belief where you think there might be many different things out there that we don't know about yet. It's kind of like when a child wonders if Santa Claus or the Tooth Fairy or a magical unicorn might actually exist even if they have never seen it. It’s being open to the possibility that anything could exist without actually committing to any one thing. Basically, it's a way of thinking that encourages you to explore new ideas without having to stick to a particular belief.