This is a hubcap. I call that a ‘wheel cover’. I call this a ‘hubcap’, because it only covers the hub. It’s also known as a ‘center cap’. I’m guessing people call it a center cap because a ‘hubcap’, in their minds, covers the entire wheel.
For a long time, most cars had stamped steel wheels that were completely covered by decorative trim. Originally, hubcaps only covered the hubs. When stamped steel wheels became the norm, the name carried over to the trim that covered the entire wheel. By making the distinction between trim that only covers the hub, and trim that covers the entire wheel, I’m being pedantic. (Or as the SO says, ‘annoying’.) I can’t help it. When I say that I’m getting new hubcaps for my Jeep (the original ones melted off the other day), I mean I’m getting the caps that cover the hub. My BIL thought I was intending to get wheel covers – even after I explained what I meant. Sometimes it takes longer to be precise. (I think he still doesn’t understand. He’s like, ‘Why don’t you just get new wheels?’ and ‘Hey, are you going to get spinners?’)
Do you differentiate between hubcaps and wheel covers?