Explanation/Reference:
/A virtual environment is a collection of virtual machines that is managed by Lab Management. You can run manual and automated tests from Microsoft Test Manager using this virtual environment. You can schedule Microsoft Team Foundation Build workflows to build, deploy, and test builds of your application onto virtual environments. Lab Management is integrated with Microsoft System Center Virtual Machine Manager (SCVMM) to enable you to efficiently create, store, and run these environments.
/You manage Lab Management environments for a team project from the Lab and Library tabs of Test Manager.

* The Lab tab provides access to the virtual environment and machines that are deployed on the host groups of a team project. A host group is a collection of one or more physical computers that are managed by Lab Management to host the environments. You interact with a host group as if it was a single computer.
* The Library tab provides access to stored environments, virtual machines, and templates that you use to create virtual environments in the team project Lab.