SDL is the abbreviation of Simple DirectMedia Layer. It is a software library written in C which provides a free, easy and platform-independent access to features needed for developing high performance games and applications. This includes easy access to graphic, sound and input device handling (keyboard, gamepad, mouse, joystick, touch screen, …)

The idea is, you create a program against SDL and it should compile on any supported platform (Linux, Windows, Mac, Android, iOS, Playstation, …) without or with minimal adaptions necessary.

Originally when referring to SDL, SDL version 1.2 was meant. It is the predecessor of SDL2 and modern SDL3. Nowadays, when refering to SDL, it depends on context if you really mean the old SDL 1.2, the successor SDL2 or the modern SDL3.

For the obsolete SDL versions and the modern SDL3 are sets of units available for Free Pascal and other Pascal dialects.