The English Wiktionary has a dictionary definition (meanings of a word) for: coalition
A coalition is an alliance, where the members work together.
Politics and government
A coalition government, in a parliamentary system, is a government made from a coalition of parties. This means the union of different political parties or groups for a purpose, usually for a short time.
In international relations, a coalition can be a group of nations united for a specific purpose, such as fighting a war.