What do you call something that's not the primary key?
User terms surrogate key and natural key for primary key as a variant.


  Surrogate Key:
  
  Surrogate keys are keys that have no
  “business” meaning and are solely used
  to identify a record in the table. 
  Such keys are either database
  generated (example: Identity in SQL
  Server, Sequence in Oracle,
  Sequence/Identity in DB2 UDB etc.) or
  system generated values (like
  generated via a table in the schema).
  
  Natural Key:  
  
  Keys are natural if the attribute it
  represents is used for identification
  independently of the database schema. 
  What this basically means is that the
  keys are natural if people use them
  example: Invoice-Numbers, Tax-Ids, SSN
  etc.


Surrogate Keys vs Natural Keys for Primary Key