chord
Several notes sounding together, heard as one object with a mood.
Several notes sounding at once, heard not as separate pitches but as one object with a mood. The smallest full chord is the triad; stack more thirds and you get sevenths and extensions. Which notes clash or fuse is decided by the intervals between them.
Learn it: Triads
The one-sentence definition at the top is the same one the Theory Aide extension shows as a tooltip inside Ableton Live. Hover any dotted term for its own.