Final answer:
A compound attribute is an attribute that contains a collection of related sub-attributes, which helps organize and reduce redundancy in a database system.
Step-by-step explanation:
An attribute that contains a collection of related attributes is called a compound attribute. This type of attribute in database systems allows one to group together related data within a single attribute, making the model more organized and reducing redundancy. For example, an address compound attribute might include street, city, state, and zip code as related sub-attributes. It helps to conceptualize data in a way that is closer to real-world representation.
Other attribute types mentioned include a class attribute, which often refers to a property shared by all instances of a class in object-oriented programming; a key attribute, which is an attribute used to uniquely identify a tuple within a relation; and an association attribute, which may be used to describe an association between classes in an object-oriented context.