A group of twelve items.
"The baker placed a dozen fresh croissants on the counter for us to take home."
In plain English: Twelve is the number that comes right after eleven and before thirteen.
"The school bus has twelve seats for students."
The cardinal number occurring after eleven and before thirteen, represented in Arabic numerals as 12 and in Roman numerals as XII.
"She counted out twelve coins from the jar to pay for her lunch."
The word "twelve" comes from Old English, where it originally meant "two left over," referring to the fact that there were two items remaining after counting up to ten. This concept traces back to a Proto-Germanic compound describing the same idea of leftovers after reaching ten.