What does the idiom 'a baker's dozen' mean?

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.
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First answer by Chicagoborn. Last edit by Darksyde. Contributor trust: 1167 [recommend contributor recommended]. Question popularity: 101 [recommend question].