In general, virtual means the quality of effecting something without actually being that something. In information technology, there seems to be a virtual version of (virtually) everything.
"Virtual" derives from the Latin "vir" ("man" in an idealized sense), from which developed the Latin "virtus" (strength, manliness, virtue). In Middle English, the adjective meant "possessed of certain physical virtues." By modern times, it had come to mean, as defined in Webster's, "being in essence or effect but not in fact."