Virtual Machine (VM) is a software program or operating system that not only exhibits the behavior of a separate computer, but is also capable of performing tasks such as running applications and programs like a separate computer.
In other words, a VM is a software application that performs most functions of a physical computer, actually behaving as a separate computer system.
A Virtual Machine, usually known as a guest, is created within another computing environment referred to as a “host.” Multiple virtual machines can exist within a single host at one time.
Source: https://www.techopedia.com/definition/4805/virtual-machine-vm