I'm self-studying music. I'm trying to learn about chord but I'm currently stuck on its definition. I've read that a "chord" is like a triad, which is 3 notes comprised of a root, a third, and a fifth. But in other definitions, a chord can be any combination of notes, as long as it is 3 OR MORE notes. So what is a chord, then, how many notes is it comprised of
Basically, a chord is comprised of 3 or more notes. Some disagree and say a chord can be made up using only 2, although that's usually called a dyad. Anyone marking this answer down due to that statement has a perfect right to explain why.
Those 3 notes together get called a triad, and can be any 3 notes at all. Obviously, some combinatios won't sound so good, and the most common combinations are 1, 3 and 5 of a major or minor scale.
Chords of more than 4 notes are often termed extensions, as they can contain extra notes, usually in what we call stacked thirds. As in C E G B D - each a third apart from the next note - 1 3 5 7 9. That will be called Cmaj9. Often, in chords that have several extensions, specific notes are omitted, partly due to clashes in sound, partly due to the fact that on some instruments - guitar, for example - all the relevant notes can't physically be played simultaneously.
So, a chord has anything from 3 to many notes in its make-up. There is no maximum number.