I am a college student and we have basic optics. I am confused with the term 'virtual' images. A virtual image proced by a lens can act like an object for another lens, but in mirrors, we say, virtual images are formed 'behind' the mirror. but, if you keep a mirror behind the one producing the image, you cant have the mirror reflect the image. Then why do we say that virtual images for a mirror are formed 'behind the mirror'?