An object-oriented relationship specifying that two classes have some relationship, but it is not an inheritance, containment, or uses relationship.
An attribute whose only purpose is to describe some feature of the objects that belong to the class.
An attribute whose purpose is to allow an object of a class to get access to an object of another class.
A term used in some object-oriented methodologies to describe an association that is not reducible to any of the other object-oriented relationships.