Virtual : rather than actual.
Virtualization is the creation of a virtual version of something, such as an operating system, a server, a storage device or network resources. In simple words, it represents an abstraction from physical resources.
In server virtualization, each virtual server runs multiple operating system instances at the same time. Server virtualization is a virtualization technique that involves partitioning a physical server into a number of small, virtual servers with the help of virtualization software.
Desktop virtualization is a virtualization technology that separates an individual’s PC applications from user’s desktop. Virtualized desktops are generally hosted on a remote central server, rather than the hard drive of the personal computer. Because the client-server computing model is used in virtualizing desktops, desktop virtualization is also known as client virtualization.
Storage virtualization is a concept in System Administration, referring to the abstraction of logical storage from physical storage . This separation allows the Systems Admin increased flexibility in how they manage storage for end users. Virtualization of storage helps archive location independence by abstracting the physical location of the data. The virtualization system presents to the user a logical space for data storage and itself handles the process of mapping it to the actual physical location.