SF2 is a sound file that is used in music sequencers. Each SF2 (soundfont) file can be multisampled, meaning you can have 1 piano soundfont that is sampled in every key, or 1 soundfont file that includes multisampled instrument sounds from an entire orchestra. It’s advisable to use Soundfonts rather than Wav files while composing music in your favorite piano roll/sequencer for the most true and realistic sound.