In KEYED access to a file, the KEY= clause specifies the contents of the key field for the record to access. The key field (also known as the key, the record key, the index or the index field) is used for building a special internal file called the key file (also known as the index file). In short, its purpose is to hold a list of information that acts much like a cross-reference from the key field to the relative record number.
Private or Public Keys are also used for encryption.
Used as a parameter in the following statements: