Firebird refers to an open-source SQL Relational Database Management System that runs on Microsoft Windows, Linux, macOS, and various other UNIX platforms.

Features:

SQL Compliance: Firebird adheres to entry-level SQL-92 requirements and the Firebird server supports the development of dynamic SQL client applications. Also, it ships with a host-language precompiler and in-engine language support for embedded SQL development in host languages like C/C++ and COBOL.

Multi-user Database Access: The key objective of Firebird is to give access to a single database to many clients at the same time. In this way, client applications can have active connections to multiple databases simultaneously. Firebird does the work of protection of cross-database transactions through a two-phase commit mechanism. Triggers and stored procedures can post-event messages to interested clients of particular events in the database.

User-Defined Functions: User-defined functions (UDF) can be written and easily stored on the server machine in external shared object libraries. The UDF is available to any client application accessing the database once it is declared to a Firebird database as an external function as if it were a native function of the SQL language.

Security: Firebird maintains a security database storing encrypted passwords and user names. It is situated in the root directory of the server installation and controls access to the server itself and all databases in its physical domain.