Thie variable contains the full path to the root folder for the installation. By default, this is set to <ROOTDRIVE>.
Note: Although many folders on the Files and folders project page are shown as subfolders of the TARGETDIR root folder (represented as Target System in the folders tree), most of them are automagical folders whose actual installation paths are determined at installation time. They may or may not end up as subfolders of the TARGETDIR root folder.
You can refer to it as <TARGETDIR>. Set automatically by the installer. Because this is a public property, you can also set it on the installer's command line.