Augmented Reality, AR as it is commonly known as, is the merging between the real world and the virtual world, often through a mobile device such as a tablet, or smartphone, or maybe a webcam, acting as the virtual camera, and on said screen virtual 3D objects are placed into positions overlaid in the real world. Some applications use image processing techniques to detect flat surfaces from the real world to place said virtual objects.
The future of AR is through worn glasses such as the Hololens, Hololens 2, and the Magic Leap headset. These are often classes as Mixed Reality (MR) headsets as they merge the 2 worlds together with some form of spatial mapping. Mixed Reality has become the common term for AR.