Learn in the textbookFundamentals and Types of Virtualization
DefinitionA virtual machine (仮想マシン) is a virtual computer, realized in software, that virtualization creates on top of a physical machine.
ExplanationEach virtual machine is given part of the physical machine's resources, and its guest OS and applications run within that share. Virtual machines are independent of one another, so a failure in one is unlikely to spread to the others. Since a virtual machine is really just files and data, it is also easy to copy or move to another physical machine.
AnalogyIt is like the units in one apartment building. There is only one building, but different people live in each unit, and noise next door rarely reaches yours.