What's meaning of dim "none"?

Hi guys and mentors,

In the section of djmodel, from Jazz hw.

what’s the meaning of dim none? batch size?
for example:
image

or, after using the function reshape:

so, after you reshape something, new dim (batch size) will be introduced? I want to reshape to 2D (3, 4) and final output will be 3D (None, 3, 4) ? wow… thank you.

In that context, “None” means that the dimension is not being defined in that line of code. Some other line of code will define that variable later.

yeah, you are right. I googled about this. I am not 100% clear when this should be introduced, but it seems like this 1st dim is the batch size… thank you.