A web-whoops, where the intended word was "account" but the fingers were faster than the brain, and the brain forgot to spell-check.
Very bad if you do it in a business letter and do not correct it, leaves the customer wondering: "What's an Aco cunt?"
(Also sounds like it may be a really unpleasant coconut.)
Dear Mr Jones,
We have recently reviewed your acocunt.....Please bring your acocunt up to date immediately!