8Bit

8 Bit Processors, the early time of Computer CPUs, the 8 Bit comes from the Address bus which can operate with 8 pins (=256 directly addressable "steps"). so the bus width is 8 Bits (means 8 switches in binary 0 or 1 state)

in music this often refers to classic computers of the late 70s and early 80s like the

Commodore C64 or the Apple II Series or even the Sinclair Computers (ZX81, ZX Spectrum etc.)

the C64 eg. had a Sound chip (SID) aboard, which is in fact a 3 voice analog synthesizer. so this also counts in as 8bit sound as well as the Gameboy or other Homecomputer Sound Chips..

There are some Hardware Boards like HardSID and Software Emulations to get the authentic Sound into modern computers, but also real Synthesizer Hardware: The Sidstation by Elektron was based on the SID Chip (which was made by the people who did Ensoniq).

There is also a Music Scene (Micromusic) and some Artist who are very 8Bit and still use C64's, Gameboys and more..