What role does the concept of foreign key play when specifying the most common types of meaningful join operations?

A foreign key is a column that references a column (most often the primary key) of another table that is used to maintain the relationship between two tables.

Explanation:

A foreign key is mainly used for establishing relationships between two tables. The purpose of the foreign key is to ensure referential integrity of the data. Only values that are supposed to appear in the database are permitted. A table can have more than one foreign key

The JOIN operation is used to combine related tuples from two relations into a single tuple.

A tuple is a single row of a table, which contains a single record for that relation is called a tuple