I can’t explain it in my own words, because I haven’t heard the term before, but Oxford dictionaries says this:
Augmented reality: A technology that superimposes a computer-generated image on a user's view of the real world, thus providing a composite view.
https://en.oxforddictionaries.com/definition/augmented_reality
And Wikipedia has an article on it: https://en.wikipedia.org/wiki/Augmented_reality