Wondering what it should be called

I was looking at a HTML element and it got me wondering. There's the
margin, the border and the padding. And then there's this space within
the padding that doesn't seem to have a name that I know of. I have
seen people refer to it as the "content". I'd have thought though that
the content is the thing that goes within this space and isn't the
name for the space itself. The content, after all, doesn't necessarily
take up all of the space within the padding. The best name I can think
of is the "content area" but I was wondering if there was a proper
name for it. Any ideas?

Appollogies if this isn't the right place for this kind of discussion.

Richard