Topic 3: Virtual.

The term virtual is a concept applied in many fields with somewhat differing connotations, and also, differing denotations.
The term has been defined in philosophy as "that which is not real" but may display the salient qualities of the real.[citation needed] Colloquially, 'virtual' is used to mean almost, particularly when used in the adverbial form e.g., "That's virtually [almost] impossible".


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The word virtual has been applied to computing and information technology with various meanings. It is used of software systems that act as if they were hardware systems[citation needed] (virtual machine, virtual memory, virtual disk), of computer-generated simulations of reality (virtual reality), and of internet gaming environments wherein entire worlds are created (virtual world) or the real world is supplemented with virtual images (augmented reality). Other applications of the word are being found constantly in this fast expanding field, such as virtual community, virtual library, and virtual class.
Early motivations for applying 'virtual' to computers (i.e., virtualization) were sharing of actual devices by many users and coordination of multiple processes, as seen with the successful use of the virtual machine approach.

http://en.wikipedia.org/wiki/Virtual