An ‘autistic focus’ is my personal term for a ‘special interest’ – you’re welcome to use it, too!
I prefer it sometimes to ‘special interest’ because of the negative associations with the word ‘special’ when used to refer to autistics. I also feel that ‘interest’ doesn’t quite do justice to the intensity of the feeling of love we have towards our focuses. For me, there’s a difference between a regular interest and a focus. We have more than just curiosity about the subjects we love – we devote ourselves to them to an extent that allistics (non-autistic people) don’t. Our focuses can be wonderful; sources of joy and comfort for us. People can mock us for how much knowledge we have about subjects that no one else seems to care about. But you don’t need to worry about what other people think! It’s good to be passionate and excited about your interests, even if they’re ‘obscure’, and it’s a wonderful thing to want to share knowledge with others!