Query optimization is the process of improving the efficiency of a database query to ensure it runs faster and uses fewer resources. When a user requests data from a database, the system must determine the best way to retrieve that information. This involves analyzing various factors, such as the structure of the data and the available indexes, to find the most effective path to the desired results. By optimizing queries, databases like MySQL or PostgreSQL can significantly reduce response times and improve overall performance. Techniques such as rewriting queries, using indexes, and analyzing execution plans help database administrators ensure that users receive their data quickly and efficiently.