Augmented reality is where what you are viewing on a computer device (computer, tablet, phone, etc) pictures or video of the real world around you but has additional stuff in it that is not real.
PokemonGo is an example of augmented reality. It uses your camera on your phone to be giving real video of the surrounding you are in, so it is live video. However it ios augmented reality because it adds the Pokemon characters in to the real images and if you were to look away from your screen you would think you could actually grab them but they have been virtually added to the picture. PokemonGo is showing the new level we can use augmented reality to mix reality (the real world) and virtual reality which has the imaginary characters.
However this is not the first use of augmented reality. People that watch football games and baseball games on TV have seen augmented reality and are sometimes surprised when they actually go and watch a game that some things are not real. For instance in football it continuously shows us a bright line across the field that is the first down line. That has been added at the TV studio and is not really there. In baseball there are ads continuously appearing on the wall behind home plate and you go watch a game in person and discover it is a plain wall. Both cases are using augmented reality.