A rootless voicing is a way of playing a chord, typically with four notes in the middle of the keyboard, that omits the root. Since the bass player is already sounding the root, the pianist uses the space for the third, the seventh and extensions such as the ninth or thirteenth. For C minor 9, for instance, a common left-hand shape is E♭–G–B♭–D: there is no C, yet the chord is unmistakable once the bass plays it. Teachers usually present two positions, one with the third at the bottom and one with the seventh at the bottom, which lets the hand move smoothly through a progression.
These voicings are closely associated with the pianist Bill Evans (1929–1980) and became standard jazz piano technique. Their soft, clustered sound, without a heavy low note, explains why so many jazz lo-fi keyboard loops feel light even when the harmony is rich.