(1) It is existent-dependent;
it cannot exist without the entity with which it has a relationship.
(2) It has a primary key that is partially or totally derived from the parent entity in the relationship.
Example: Assume you wish to know information on students and possible siblings they might have. You begin with two tables: STUDENT and SIBLING. In this case, the table SIBLING is dependent on STUDENT to exist. SIBLING by itself has no meaning