Stereoscopy is a method by which the illusion of 3D is conveyed through a two dimensional medium. That can be video, images, a VR headset or blender's 3D view.
Stereoscopy is a broad term covering over stereo 3D, virtual reality, multi-view.
This ability was added to blender in version 2.75. You can learn more about blender's stereoscopy features in the manual.