Comment by kaoD

TBH "definition" depends on the theory from which you're looking at the notes.

In the eyes of the Common Practice two simultaneous notes are not chords; in rock they most definitely are; in EDM you don't even care, since timbre is all that matters; in jazz you'd say "it depends" (e.g. might even be a triad with an omitted 5th... depending on context!)

Music theory is too post-hoc.