Eight-to-fourteen modulation
Eight-to-fourteen modulation (EFM) is a data encoding technique – formally, a line code – used by compact discs (CD), laserdiscs (LD) and pre-Hi-MD MiniDiscs. EFMPlus is a related code, used in DVDs and Super Audio CDs (SACDs).
Source: Wikipedia — Eight-to-fourteen modulation (CC BY-SA 4.0)