I think these are sometimes called cutaneous horns. They're growths of keratin, like nails, but they don't have any blood supply or tissues inside them, so it's fine to trim them off. They will probably grow back unless a vet removes them, and they might be a little thicker or weirdly shape so nail trimmers don't always fit neatly around them. Sometimes they bother the cat, and it's good to trim them, but sometimes the cat doesn't mind. I think it's believed there's a connection between them and some viruses, but not always.
My cat has them on her carpal pads. She's also FIV positive, so I wonder if that could be the cause. I'm going to mention it the next time she goes to the vet for a check-up just to make sure they know about it.
This is what hers look like: