The Roland TR-808 drum machine, released in 1980, had a kick drum with a long, tuned decay. Producers learned to tune that kick to notes and play basslines with it. Today "808" usually means a long sub-bass hit that acts as both kick and bass.
Glides between notes, distortion and long tails are signatures of modern 808 programming.
Using it in a prompt
Ask for "gliding 808s" in trap or drill, "distorted 808" for phonk, or "soft 808" when it should sit under melody.