In relational databases, a primary key uniquely identifies each row in a table. Sometimes, a single column isn't enough to guarantee uniqueness. A composite key, or compound key, is a primary key composed of multiple columns working together. This approach is essential when a single column isn't sufficient to uniquely identify a record. For example, in an order table, you might have customer ID and order date. A single customer could place multiple orders on different dates. Therefore, a composite key using both customer ID and order date is necessary to uniquely identify each order. This ensures that no two orders from the same customer on the same date are accidentally duplicated or overwritten. Composite keys are particularly useful in scenarios where a single column isn't sufficient to represent the unique identity of a record, such as in situations involving multiple attributes that need to be considered together. This approach is crucial for maintaining data integrity and preventing data redundancy.