Ok, the word is "subpoena." Pronounced sub-pee-nuh.

The way traffic court generally works is that if you plead guilty then the judge reduces your sentence. Basically they reward you for taking time out of your day and showing up to pay court fees, with a better driving record than you would have had if you just mailed in the fine for the ticket.

Now it sounds like you have another hearing and the cop is going to show up with results from his speed gun saying that you were in fact going the speed written on your ticket. If you say to the judge, "but I swore I was only doing 80" they will not believe you.