PostgreSQL is an open-source object-relational database management system (ORDBMS). Some key features include ACID compliance, MVCC for concurrency control, write-ahead logging for crash recovery, and point-in-time recovery. It supports many advanced features including foreign keys, triggers, views, complex queries and stored procedures. PostgreSQL works on Linux, Windows, Mac OS, and many other platforms and integrates well with programming languages like PHP, Python, Ruby and Java.