piano chord
Em7♭5
E1G♭3B♭♭5D♭7
A diminished triad with a minor seventh rather than a diminished one — half diminished, and not the same chord as dim7.
What is true of it
Em7♭5 is E, G, B♭ and D — 1, b3, b5 and b7 counted from E.
These are also the notes of Gm6/E. Which name is right depends on what is underneath and what came before — the notes alone do not decide.