Roland GS, or just GS, sometimes expanded as General Standard[1][2] or General Sound,[1] is a MIDI specification. It requires that all GS-compatible equipment must meet a certain set of features and it documents interpretations of some MIDI commands and bytes sequences, thus defining instrument tones, controllers for sound effects, etc.
In addition to the simpler General MIDI standard, GS defines 98 additional tone instruments, 15 more percussion instruments, 8 more drum kits, 3 effects (reverb/chorus/variation) and some other features.
The Roland SC-55 was the first synthesizer to support the GS standard.