Shader

Shader (verb to shade) term have several meanings.

1. Program for 3D rendering pipeline which could be written in various shader languges (GLSL, HLSL, Cg, ARB etc.). There is vertex shader, pixel shader, geometry shader etc. This is most official meaning.

2. Quake 3 Material. In Id Tech 3 materials are named shaders (this includes many techical papers that describe MD3, Q3BSP etc.). So after q3, sometimes materials they get called as shaders, which is not correct. Since Darkplaces engine's material system using Id Tech 3 material approach as a base, it's materials sometimes called shaders too (material files extension is .shader).

3. Programmable block for anything that is processed in realtime. There is sound shaders, light shaders, entity shaders etc. Shader is different from script as it runned in realtime.