General MIDI,
+++ GM +++, is a standardized list of
128 instrument patches and sound effects. The goal of the list is to make sure when you call instrument patch # 33 the GM compatible synth loads an acoustic bass instrument patch.
Before the list was adopted every synth module instrument patch list was defined by the synth manufacturer. This led to issues where the wrong instrument sound would get loaded when patch changes were made during a performance.
General MIDI 2, GM2, raises the number of standard instrument patch and sound effect names to 256.
Both Roland and Yamaha have additional naming standards, GS and XG respectively.
+++ HERE +++ is a pretty good comparison of the various MIDI patch name conventions.