[Definition] A non-primary key that can be used to identify only one row in a table. Alternate keys may be used like a primary key in a single-table select. [Key Name] 
Alternate
S i m p l e
C o n c a t e n a t e d
C o m p o u n d
C o m p o s i t e
N a t u r a l
S u r r o g a t e
C a n d i d a t e
P r i m a r y
A l t e r n a t e
F o r e i g n