A Virtual Machine (VM) is a software program that allows a vitrual Operating System to run on top of whatever OS is controlling the hardware. One major benefit of a VM is if it crashes, it can be quickly and easily started from a saved safe state. Multiple virtual machines can also exist within a single host at one time, and can be run cheaply from the cloud by services like Amazon's AWS.
A Virtual Network Computing (VNC) is a graphical desktop-sharing application that uses remote frame buffer protocol to remotely control another computer. This form of desktop sharing transmits keyboard and mouse events from one system to another over the network based on screen updates. -techopedia
Voice over IP (VoIP) is the technology for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. -Wikipedia