Keys in DBMS

Super key: An attribute or set of attributes that uniquely identifies an entity–there can be many of these
Composite key:A key requiring more than one attribute

Candidate key: a superkey such that no proper subset of its attributes is also a superkey (minimal superkey – has no unnecessary attributes)

Primary key: The candidate key chosen to be used for identifying entities and accessing records.  Unless otherwise noted “key” means “primary key”

Alternate key: A candidate key not used for primary key
Secondary key: Attribute or set of attributes commonly used for accessing records, but not necessarily unique
Foreign key: An attribute that is the primary key of another table and is used to establish a relationship with that table where it appears as an attribute also.