Spaced repetition which is a learning technique that incorporates increasing intervals of time between subsequent review of previously learned material in order to exploit the psychological spacing effect.
Apprentice: This item is quite new for you.
Guru: You know an item fairly well.
Master: You should be able to recall these items easily. Burned: This item is “fluent” in your brain. The answer comes with little-to-no effort. You will remember this item for a long, long time. Items that are “burned” no longer show up in reviews.