What is the purpose of the FOREIGN KEY in MySQL? Explain with a suitable example.

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The FOREIGN KEY is used to create a relationship between two tables by linking a column in one table to the primary key of another table, ensuring only valid, matching values are stored. Example: In a Marks table, Student ID is a Foreign Key that connects to the ID column in the Student table, ensuring that marks can only be entered for students that already exist in the Student table.