Foreign Key
In plain terms
A column that references the primary key of another table.
Going deeper
A foreign key links rows across tables and enforces referential integrity, ensuring relationships stay valid. It connects related data.
Under the hood
Prevents orphaned records and supports cascade actions; central to relational data modeling.
Examples
order.customer_id → customer.id, joins, referential integrity, relationships.
Think of it like...
Like a cross-reference pointing from an order to the customer who placed it.