From ACT Wiki
1. Organisational structures.
An organisation owned and controlled by its customers - who are members of the mutual organisation - although day to day management will often be undertaken by professional managers, especially in larger mutuals.
Building societies and credit unions are mutual organisations.
The members do not normally contribute directly to the capital of the organisation.
Rather, they derive their rights to vote and to surpluses, from their customer relationship.
Agreed by, or affecting, both parties to a contract or other arrangement.