This was the name of the first soundcard
for the IBM PC
Before the Soundblaster card revolutionized PC audio, the Adlib card was already widely used and supported by games.
An AdLib card basically only consists of a Yamaha YM3812 synthesizer chip (also known as the OPL-2 chip) memory mapped at I/O location 0x388. This chip offers 9 FM voices, with 2 operators each and 5 percussive voices (i.e. synthesized drum sounds, that weren't used a lot, because they sounded so bad).
The AdLib card didn't contain any DAC or ADC hardware, so playback and recording of samples was not possible.
The Soundblaster card that came out later was fully AdLib compatible, and therefore the AdLib standard became a PC legacy subsystem, that has only recently been given up.