From Tungsten Graphics
Tungsten Graphics Shader Infrastructure
TGSI defines an extensible binary representation for shader language programs which forms part of the Gallium3D driver interface. TGSI instructions have been designed to allow quick translation of most known shading languages into a binary representation. Quick translation is a requirement as the Gallium3D drivers may be implemented on top of any one of an number of arbitary third party compilers, each with their own preferred internal representation.