piano chord
C♯7
C♯1E♯3G♯5B♭7
Major triad, minor seventh. The chord that wants to resolve a fourth up.
Written the other way round it is D♭7 — the same twelve keys on a piano, a different piece of notation.
What is true of it
C♯7 is C♯, E♯, G♯ and B — 1, 3, 5 and b7 counted from C♯.
On an instrument that cannot reach all 4, the 5 goes first, in that order.