When humans perceive the environment around them, each eye sees a different perspective image. These two images give rise to the perception of true depth. Most printed images which look 3D are classified as monoscopic images.
Monoscopic images try to simulate depth by using shadows and rendering techniques.
A stereoscopic image, on the other hand, appears to have real depth where objects can even seem to leave the surface of the display device and hover in the middle of the room. A stereoscopic image is composed of a right perspective frame and a left perspective frame - one for each eye. When the right frame is viewed by your right eye and the left frame is viewed by your left eye, your brain will perceive a true 3D view. The difference between simulated 3D and stereoscopic 3D is that in stereoscopic 3D a distinctly different image is being shown to each eye simultaneously. The images represent two different renderings of an idenical environment htat have been captured from positions that correspond to the location of the left and right eye.