A LEFT JOIN is a type of SQL operation that combines rows from two tables based on a related column. It returns all records from the left table and the matched records from the right table. If there is no match, the result will still include the left table's record, but with NULL values for the right table's columns. For example, if you have a table of customers and a table of orders, a LEFT JOIN will show all customers, including those who haven't placed any orders. This way, you can see every customer, even if they have no corresponding order data.