Identifying keys

A key that is made up of one field is a simple key. All other keys are combined keys. There are two types of combined keys, compound and composite:

Simple key: key that consists of one field

Combined key: key that consists of more than one field

Compound key: combined key in which each field is itself a simple key (of another entity)

Composite key: combined key, that is not a compound key

A new term I have made up myself:

Concatenated key: a simple key, that is the concatenation of the fields in a combined key