piano chord
B♭maj7
B♭1D3F5A7
Major triad with a major seventh: a half step below the root, an octave up.
Written the other way round it is A♯maj7 — the same twelve keys on a piano, a different piece of notation.
What is true of it
B♭maj7 is B♭, D, F and A — 1, 3, 5 and 7 counted from B♭.
On an instrument that cannot reach all 4, the 5 goes first, in that order.