Spaced repetition is a learning technique in which material is reviewed at spaced intervals, timed so that each review comes as the learner is about to forget it.
According to the history published on SuperMemo's own website, Piotr Wozniak formulated his first repetition spacing algorithm, later known as SuperMemo, in 1985 and began learning with it on August 25 of that year. He wrote SuperMemo 1.0 for MS-DOS in Turbo Pascal and began repetitions with it on December 13, 1987. The same account marks 1985 as the birth of computational spaced repetition, "the technique in which knowledge is reviewed in optimum intervals that are determined by a computer."
That history calls the Leitner cardfile, set out by Sebastian Leitner in his 1972 book So lernt man lernen, a precursor of spaced repetition because it uses increasing intervals between reviews. It describes Hermann Ebbinghaus's 1885 experiments on his own memory as possibly the first step toward SuperMemo, while calling the claim that Ebbinghaus invented spaced repetition a myth.
The flashcard program Anki, per its manual, bases its spaced repetition system on SM-2, an older version of the SuperMemo algorithm, and has integrated a newer algorithm called FSRS as an alternative. In language learning, Pimsleur calls graduated interval recall, one of the core aspects of 📝the Pimsleur Method, "an application of spaced repetition."