What does $VERSION mean in "./configure --with-realtime=/usr/realtime-$VERSION"?

Hi
According to what written in LinuxCNC documents to build for the RTAI realtime platform, requires to pass this option to ./configre: --with-realtime=/usr/realtime-$VERSION.
I want to know that what does $VERSION refer to? And should we write something instead or leaving the same word is enough?
And it's necessary to note that the real path of "realtime" is "/usr/realtime" and has no additional like dash or number.

It might auto-substitute, depending if $VERSION is defined in your environment.

But it is probably simpler to actually use the path to the realtime system installed on your machine. (which you can find by simply looking in /usr/ )