A chord symbol says what notes; a voicing says how to arrange them. Jazz players rarely stack a chord root-position: they play a shell (root-3-7, the 5th tossed), a rootless voicing (3-5-7-9, letting the bass imply the root — the Bill Evans left hand), a quartal stack of fourths (the "So What" sound), or a drop-2 / drop-3 spread (drop one inner voice an octave — the guitarist's move). Type a seventh chord and hear each. For the voice-leading rules underneath, see Voice Leading.