1-1(one-to-one), One-to-many (1-M), Many-to-Many (M-M)

1-1(one-to-one) is a relationship between two entities.

One-t- Many (1-M) is a relationship in which each node can have only one parent, but can have multiple children, that means an entity can have multiple relationships with other entitles in the database.

Many-to-many (M-M) is a relationship in which a record can have multiple parents and multiple children (every entity can be related to a number of entities).