adjective Of a class member: capable of being overridden with a different implementation in a subclass.
adjective Pertaining to a theoretical infinitesimal velocity in a mechanical system that does not violate the system's constraints; also, of other physical quantities: resulting from such a velocity.
virtual displacement; virtual work
adjective Pertaining to a theoretical quality of something which would produce an observable effect if counteracting factors such as friction are disregarded; specifically, of a head of water: producing a certain pressure if friction, etc., is disregarded. Chiefly in virtual focus: of a focus or point: from which light or other radiation apparently emanates; also, of an image: produced by light that appears to diverge from a point beyond the reflecting or refracting surface.