Coo may be:
- A noun and verb denoting the call of pigeons.
- An interjection of surprise and admiration.
- A derivative of the word "cool"; it has a similar usage but tends to be more sincere where "cool" is often used in a dispassionate manner as mere acknowledgement.
or refer to:
- Coo, a municipality in the Belgian province of Liège
- CoO, cobalt(II) oxide, a chemical with formula of CoO.
COO is a three letter acronym, and may stand for:
- Calgary Olympic Oval, a Canadian ice rink
- Chief Operating Officer or Chief Operations Officer, a high ranking corporate official
- Cell of origin (telecommunications)
- Country of origin
- Carboxylate, a type of anion
