PostgreSQL is an open-source, object-relational database management system (ORDBMS) known for its robustness, scalability, and SQL compliance. It supports advanced features like ACID (Atomicity, Consistency, Isolation, Durability) transactions, complex queries, and a wide range of data types. PostgreSQL is highly extensible, allowing users to define custom data types, functions, and operators. It is often used for web, mobile, and enterprise applications due to its performance, reliability, and support for large datasets. Additionally, PostgreSQL is widely appreciated for its strong community support and active development.