It's better thought of as a tax that funds the BBC, but it can't be called a tax because it's not run by the government.

It's an outdated idea though that doesn't make any sense in this era because it means that technically if you want to watch any live TV at all then you have to pay the BBC money even if you don't watch anything by them.

Or you could just not answer the door in the extremely rare case that any enforcement officers actually come around and instead watch TV for free.