PostgreSQL, also known as Postgres, is a free and open-source relational database management system emphasizing extensibility and SQL compliance. It is widely used for its reliability, robustness, and performance. PostgreSQL supports various data types, indexing methods, and query optimization techniques, making it suitable for a wide range of applications including web development, data warehousing, geospatial analysis, and business intelligence. PostgreSQL's advanced features include support for transactions, concurrency control, replication, partitioning, and full-text search. It provides a rich set of extensions and user-defined functions, allowing developers to customize and extend its functionality to meet their specific requirements. PostgreSQL is known for its active community, frequent updates, and strong emphasis on standards compliance. It is used by companies such as Apple, Cisco, Spotify, and Reddit to power their mission-critical applications and services.