Originally Posted by iWonder
By the way, what would an A2(no.3) chord be? Is this Asus2 played on the 7th fret?
"A2(no 3)" is pretty clearly Asus2, wherever it's played. Adding the "no 3" is (I guess) confirmation they don't want an Aadd9, in case of the confusion expressed above (rightly) about "A2".

In practice, Asus2 sounds very like Aadd9, so there wouldn't often be an issue. Where it would matter would be where the A2 was standing for an Am chord (in a place where you would expect a diatonic Am). If someone played an Add9 instead, it would certainly sound wrong.

This thread is of course 3 years old now... ... but I would add some other thoughts:

In my experience, "sus" in jazz is an abbreviation of "sus4" (and often assuming "7sus4", or even "9sus4"). I've never seen a "sus2" or "2" chord in any jazz chart. (I can't even remember seeing an "add9", although that would be less unlikely.)
In jazz, they would regard a sus2 as an inverted sus4. Eg, the notes C-D-G would be seen as a kind of Gsus4, not Csus2.
Jazz chord players are extremely reluctant to lose the 3rd of a chord unless they have to. In a sus4 there is a clear clash with a lower major 3rd. In a sus2, there is no such clash. A C-D-G chord (with C root) could easily have an E added in there; there's no good reason to leave it out.
Mark Levine's "Jazz Theory Book" has - in its 400+ pages - no mention of sus2 chords at all, nor add9s. He mentions only "sus" (which could be 7sus4, 9sus4 or even 13sus4, and are usually considered as mixolydian chords) and "susb9" (7sus4b9 in full, a phrygian chord). The message is that jazz has no use for a sus2. And little, apparently, for an add9.

Rock, of course, is a different matter! Sus2s are popular as a kind of consonant extension of power chords.

As for the idea that a sus2 should (in theory) omit the root, because a suspension resolves downward, that's an interesting idea, but is not how I see it. A suspended 2nd (or 9th) can easily - and often does - resolve upwards. At least, that would be the logic in calling a 1-2-5 chord "sus2", omitting the 3rd in expectation of the 2 resolving up to it.
In fact the 2nd (or 9th) in an "add9" chord can also end up resolving up or down (to 3 or 1). The 3 doesn't need to be omitted from the initial voicing.

Of course, in modern music (as pointed out above) sus2s and sus4s alike often don't resolve anywhere. We just don't have an alternative term for a suspension that is merely a modal colour and not a functional dissonance.

A "sus2" is hardly a dissonance anyway. A lot of the time in rock it's played as two stacked 5ths (one of Hendrix's favourite sounds), about the most consonant triad imaginable.