VM stands for Virtual Machine. Project managers or the Copilot will set up the environments for competitors. The competitors can use the credentials provided to access the VM. Competitors can use their VMs code, debug and finally check-in the solutions. After all competitors check-in their solutions, the VM will test each of the solutions.
Sometimes it is time-consuming to configure locally the environment of the contest. To avoid this problem, and to be more proficient, TopCoder is using VMs to enable competitors working on.