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Composite key
A composite key is a primary key that consists of two or more columns.
Foreign key
A foreign key is a column (or set of columns) in one table that references the primary key of another table.
Linking entity
An entity placed between two entities to resolve a many-to-many relationship, replacing it with two one-to-many relationships. It becomes a junction table holding one row per pairing, keyed on the two foreign keys together.
Primary key
A primary key is a unique identifier for each record in a table.
Referential integrity
The rule that every foreign key value must either match an existing primary key value in the referenced table or be NULL, so no row can point at a record that does not exist.