An algorithm often used to increase the rate of memorization, improve durability of memory, and impress friends at board game parties. It is often visualized with the following graph:
There’s even a whole comic about it.
I am currently wrangling with the effects and implications of using spaced repetition to learn. Posts on this site tend to lean more toward the critical, but that is only to act as a counter-weight to the rest of the internet which seems to see mostly reasons to use it.