Virtualenv was for me until 2020 a python-default tool for creating isolated virtual environments for python projects.
Virtualenv was always easy to handle and known as a mature pythonic tool under python developers.
But now, I think pipenv is stable and known enough to switch to it.
Python virtualenv or venv are the short forms of virtual environment.
Virtualenv is useful for different projects with unique requirements for each of them, like versions of python or at least different versions of Python libraries.
So they run parallel on a same system in separated from each other environments without any conflicts between them.