Database indexing is a technique used to improve the speed of data retrieval operations on a database. It works like an index in a book, allowing the database management system to find and access data quickly without scanning every row in a table. By creating an index on specific columns, the database can locate the desired information more efficiently. When a query is executed, the database can use the index to jump directly to the relevant data, significantly reducing the time it takes to return results. However, while indexing speeds up read operations, it can slow down write operations, as the index must be updated whenever data is added or modified.