MP2
MPEG-1 Audio Layer II — MP3's older, simpler sibling, which stayed on in radio and TV long after music libraries moved on.
Standardised in 1993 in the same document as MP3, and derived from MUSICAM, which IRT, Philips and CCETT had developed for digital radio. Layer II splits the signal into 32 sub-bands and spends bits where the ear will notice, but lacks Layer III's MDCT and Huffman coding. It needs more bitrate for the same quality; in exchange, encoding is cheap and robust against bit errors.
That made it the choice for the original DAB, for DVB television and for Video CD, and it appears on plenty of DVDs. It survives in broadcast chains because nobody replaces working transmitter gear just to make files smaller.