PostgreSQL is an open-source, highly extensible relational and object-relational database management system. On Debian 11, it installs and configures easily through official repositories, offering robustness, performance, and security. With support for ACID transactions, complex queries, and scalability, it's ideal for applications that require reliability. Additionally, PostgreSQL allows the integration of extensions and custom functions to meet various needs. Its active community provides regular updates and detailed documentation.