I did a survey of what various tools call this "place" / directory
virtualenv: virtualenv / virtual environment / venv
nodeenv: "node.js virtual environment" / virtualenv / virtual environment
nave: "Virtual Environments for Node" / navedir
npm: root / prefix
rvm: doesn't really work the same way, but: environment / gemdir / home

So not a whole lot more help from those... though I do sort of like prefix or install_prefix