Database indexing is a technique used to improve the speed of data retrieval operations on a database. It creates a data structure, called an index, that allows the database management system to find and access data more quickly, similar to how a book's index helps locate information without reading the entire book. When a database is indexed, it organizes the data in a way that reduces the amount of time needed to search for specific records. This is especially useful for large databases, where searching through all the data can be slow and inefficient.