What is Spaced Repetition?
TL;DR: Spaced repetition is a study technique that reviews information at gradually increasing intervals. Instead of cramming everything at once, you review material just before you'd forget it — strengthening the memory each time.
The spacing effect was discovered by Hermann Ebbinghaus in 1885. Modern spaced repetition systems (SRS) use algorithms to schedule reviews: new material reviewed after 1 day, then 3 days, 7 days, 14 days, 30 days. Each successful recall extends the interval.