Answer:
There are thirteen (13) items in a baker's dozen.
The term originates in England, where an Assize of Bread and Ale during the reign of Henry III. A baker that was found to have cheated a customer by not providing enough loaves (or cakes or buns, etc.) was liable to lose a hand by the axe. To prevent this, bakers baked a dozen in sets of 13 instead of 12; this extra item safeguarded against one being lost by burning, eating, theft or simple loss. If it survived, it was a freebie that gained trust in the baker.