piano chord
B♭add9
B♭1D3F5C9
A major triad with a ninth added and no seventh — which is what tells it apart from a ninth chord.
Written the other way round it is A♯add9 — the same twelve keys on a piano, a different piece of notation.
What is true of it
B♭add9 is B♭, D, F and C — 1, 3, 5 and 9 counted from B♭.
On an instrument that cannot reach all 4, the 5 goes first, in that order.