Spaced repetition is a learning technique that incorporates increasing intervals of time between subsequent review of previously learned material; this exploits the psychological spacing effect. Because of its nature, it is particularly effective in learning vast quantities of facts, such as foreign-language vocabulary.
Spaced-repetition programs include Anki, SuperMemo, OpenCards, and Mnemosyne, among others.
Questions about the application or usage of spaced-repetition programs, or that have to do with optimizing ones usage of this technique should have this tag.