PostgreSQL is a Free object-relational database server (database management system), released under a flexible BSD-style license. It offers an alternative to other database systems. Similarly to other open-source projects such as Apache, Linux, and MediaWiki, PostgreSQL is not controlled by any single company, but relies on a global community of developers and companies to develop it.

PostgreSQL's unusual-looking name makes some readers pause when trying to pronounce it, especially those who pronounce SQL as "sequel". PostgreSQL's developers pronounce it /po?st ???s kju? ?l/. It is also common to hear it abbreviated as simply "postgres", which was its original name. The name refers to the project's origins as a "post-Ingres" database, the original authors having also developed the Ingres database.