What does AC-1, AC-2, and AC-3 mean?

AC-1, AC-2, and AC-3 meaning in Computer Science Dictionary

Dolby AC-1 had been the first electronic coding technology introduced in 1987, A development that would later on be HDTV. Later in 1989, Dolby launched AC-2, which had a better audio high quality and a lower bit-rate. Eventually, in 1991, Dolby introduced AC-3, which include 5.1 channels and operates at 320 kbps.