10.8Half-diminished notation

You may see:

Cø7

or:

Cm7♭5

They mean the same chord:

C E♭ G♭ B♭

The symbol ø literally looks like a slashed diminished circle.

This is called:

half-diminished seventh

A useful way to think of it:

minor 7 chord with a flattened 5th

So:

Cm7:

C E♭ G B♭

lower G:

G → G♭

and you get:

Cm7♭5