In the reputation tab on my profile, it shows -10 for "User was removed". Obviously my account was not removed, so I don't understand what this means. Perhaps it's a bug and a post of mine was removed? If so, which?
The account of a user who had voted on your question has been deleted. Sometimes users do this themselves, rarely we have to do it for them.
When they delete their account, everything they touched goes away with them. See also What does "user was removed" mean and why did my reputation change because of it?