A Suspended 2nd
sus2
0 - 2 - 7Root + major 2nd + perfect 5th
About A Suspended 2nd
Asus2 is A major with the third removed and the second put in its place — A, B, E. Nothing tells the ear whether the chord is major or minor, and that neutrality is the point: it fits over both, which is why it appears in so many songs that want movement without commitment.
The notes
A, B, E. The B is a major second above the root, sitting where the C♯ of A major would be. With no third, the chord has no mode — it is neither bright nor dark.
On guitar the shape is one finger: the standard A with the ring and little fingers lifted, leaving the B string open. That economy is why the chord shows up in strumming patterns as a passing colour.
How it is used
Almost always in motion. A held A that alternates with Asus2 and Asus4 is one of the most common figures in acoustic guitar music, because all three shapes share a hand position and only one finger moves.
Held alone, the chord sounds open rather than unresolved — unlike a sus4, which leans, a sus2 simply sits. That difference is why the two are used in different places despite the shared name.
Where it shows up
Folk, indie and fingerstyle in the key of A or D. In the second key it appears as the V, where the missing third makes the dominant less insistent.
It also appears in drop tunings and open-string writing, where the sound of an unfretted string ringing against a fretted one is the whole texture.