What is cardinality in the context of databases?

Cardinality in databases defines the number of relationships between records in two tables. It describes how many instances of one entity (record in one table) can be associated with instances of another entity (record in another table).

Main types of cardinality:

• One-to-One: Each record in one table is related to at most one record in the other table, and vice versa.
• One-to-Many: Each record in one table can be related to multiple records in the other table, but each record in the other table is related to at most one record in the first.
• Many-to-Many: Each record in one table can be related to multiple records in the other table, and vice versa. This is usually implemented via a junction table.

Cardinality is important for proper database schema design, foreign key definitions, and maintaining data integrity.