Virtualization Software for Linux: In computing, virtualization has been described in a variety of ways. But to simplify its meaning or to make it more casual I should say; virtualization is creating a virtual (not actual) form of a stuff to make it into something that is functional and efficient. For example, you create or virtualize an operating system to make it run as guest inside the host operating system without the need for additional hardware. Some other forms of virtualization:

Server virtualization - emulation of server resources that includes individual physical servers, processors, and operating systems