piano chord
E♭6
E♭1G3B♭5C6
A major triad with a sixth added. The same four notes as a minor seventh chord a third below.
Written the other way round it is D♯6 — the same twelve keys on a piano, a different piece of notation.
What is true of it
E♭6 is E♭, G, B♭ and C — 1, 3, 5 and 6 counted from E♭.
These are also the notes of Cm7/E♭. Which name is right depends on what is underneath and what came before — the notes alone do not decide.
On an instrument that cannot reach all 4, the 5 goes first, in that order.