Surrogate Key
An artificially generated identifier with no business meaning. It exists solely to uniquely identify a Tuple within a Relation such as UserId.
Example:
| UserId | UserName | Password | |
|---|---|---|---|
| 1 | AJones | alex.jones@abc.com | ######## |
| 2 | BSmith | bob.smith@def.com | ######## |
| 3 | CBloggs | chris.bloggs@xyz.com | ######## |
In the table above UserId could be used as a unique identifier as all entries are unique, however it has no real world meaning.