What counts as a "special interest"?

I like a lot of things but I don't think I'm obsessive about any one thing the way many autistic folks are known to be. I used to collect things like marbles and popsicle stick jokes as a kid, and now I get really into a show or video game for as long as I'm watching or playing (however many days it takes to finish it, it's at the forefront of my mind and all I want to do is consume more of it). But I don't buy a bunch of stuff about it or spend all my free time on it after I'm done with it. I also don't think I'm particularly knowledgeable about the things I like (I wish my memory was better). Is that normal? I know everyone's different but I'm curious if others here don't quite fit the usual "special interest" mould.