Dozen is another word for the number twelve. It originates from the Latin word duodecim. Twelve dozen are known as a gross. Twelve gross (1728) is called a great gross, a term most often used when shipping or buying items in bulk. The use of twelve as a base number, known as the duodecimal system, probably originated in Mesopotamia.
The dozen is convenient because its multipliers and multiples are convenient: 12 = 3 * 2 * 2, and 360 = 30 * 12.
The French word douzaine means "about twelve" and is part of a family of words with similar meanings, e.g. vingtaine - "about 20" centaine - "about 100" etc...
A baker's dozen, also known as a long dozen, is thirteen.
See also