It is short for "documentation" fee. This is an addendum or additional fee assessed by the car dealer supposedly for paperwork, filing and other various items that have to go with your car purchase.  The fee you were charged is pretty average.  It is really pure profit by the car dealer.  AT this point in time I am not sure what you can do, unless there is a three day right of rescission of the contract in your state (easy enough to check on the state attorney general's site most likely) and if you are within the three days bring it in and say you do not want it.  See if the dealer will refund you the DOC fee for fear of losing the whole deal.  Good luck to you.