Dozen (noun)

1. A group or set of twelve things.
2. A size of a package or quantity that consists of twelve items.
3. Twelve as a number or quantity.
4. A collection or group of twelve items considered as a unit.
5. A series of twelve similar events or actions.

Origin:

Middle english: from old french dozeine, based on latin duodecim "twelve".

Examples:

1. A dozen eggs in a carton.
2. A dozen roses in a bouquet.
3. A dozen dollars in my pocket.
4. A dozen books in a set.
5. A dozen goals scored in a game.