When people talk about how many drawings are in an episode of an anime, does that take into account any 2nd Key or inbetween drawings? Or is it just for keframes?

normally is counted by twos. (24frames/2)

Inbetweens are counted. Every different drawing is counted. A single frame that you see in the final animation video, might have been a composition of multiple layers during its production. As in, background scenery on first layer, a flying bird on second layer, a walking human on third layer and so on. Any change in drawing in any of these layers would be counted as a new frame. But if one layer is shifted or moved along the other, like a car plainly moving from left to right on a road, it isn't using any new drawing, so they won't be counted.

This is assuming inbetweens are hand-drawn. If the animation is using mechanical inbetweens inserted by softwares like cacani, then it might need the question to be a bit more specific.