Apparently, this directory is also referred to as the Visual Studio IDE directory.
Beginning with Visual Studio 2017, the path of the root directory includes both, the versionandedition, aka offering, (such as professional or community).
Thus, the path to this root directory might be (and with a default installation is): C:\Program Files (x86)\Microsoft Visual Studio\version\edition.
With VS 2017 and later, this root directory can be found with the vswhere.exe utility.
This directory contains sub-directories such as
Common7
DesignTools
DIA SDK (The Microsoft Debug Interface Access Software Development Kit (DIA SDK) provides access to debug information stored in symbol (.pdb) files generated by Microsoft postcompiler tools.)