Chiptune
Also said as 8-bit music, Chip music
Music written for, or in the style of, the sound chips of old consoles and computers. Those chips have only a few voices, each playing one note at a time, so every limit is heard.
It is an instant signal of an era, and the limits make it very cheap to run. Fast arpeggios that fake chords are its signature, born because no channel could hold a chord.
Say it
“Write the score for NES limits: two pulses, a triangle and noise, one note per channel. Fake the chords with arpeggios and put the bass on the triangle.”
Where you’ve seen it
Shovel Knight's score, by Jake Kaufman with Manami Matsumae, was written for the NES chip plus the VRC6 expansion, eight channels in all. The VRC6 only ever shipped on the Japanese Famicom, so the sound is authentic to hardware most players never owned.
Not to be confused with retro-sounding music
True chiptune stays within a chip's real channels. Plenty of retro-styled scores use modern synths and reverb, which the old hardware could not have played.