(1) In a relational database, a key that uniquely identifies one row of a database table. See also constraint, unique key, foreign key.
(2) An object that uniquely identifies an entity bean of a particular type.
(3) In each record of a VSAM KSDS, an identifying field. The key of each record is a field in a predefined position within the record. Each key must be unique in the data set.
(4) In a federated system, a unique key that is part of the definition of a nickname and that the optimizer uses to improve query performance. This key is not validated when operations such as insert and update are performed.