Question

Okay so me and my SO were messing around and he was fingering me. While he was in me he said he felt something that felt like a ball. Does anyone know what that is?? I'm now wondering what that is. And please don't say I need to educate my self. I'm 21 and where I attended school we didn't get taught much about sex so most of the things I know is because I taught myself or at the doctor