DLS (Downloadable Sounds)
The MIDI industry's standard format for sampled instruments, letting a MIDI file bring its own sounds instead of trusting whatever the receiver has.
General MIDI guaranteed that program 1 is a piano but said nothing about which piano. The MIDI Manufacturers Association answered in 1997 with DLS Level 1: a RIFF-based file holding samples, loops, key ranges and simple envelopes that any compliant synth can load. Level 2 later added filters, more modulation routings and layering per key. The design is close kin to Creative's SoundFont, and the two formats competed for the same niche.
Microsoft built DLS into DirectMusic, and the file gm.dls, full of Roland samples, still ships with Windows. Mobile DLS later underpinned polyphonic ringtones, a brief but very profitable era.