What is the middle section of a cave called?

The middle section of a cave is NOT called twilight. The description itself states that twilight is near the entrance. That is not the middle. The middle of caves I've been in are dark.

YSL, maybe it depends on the size of the cave

i'm scared of millipedes

Surely, whether the middle of a cave is dark or not depends on the size of the cave and the size of the entrance - if the cave is small and entrance wide then the middle would be light and conversely if the cave system is large and the entry narrow, then the middle would be dark.

Luckily I have been spelunking.