Spaced repetition

Spaced repetition is a learning technique usually using flashcards, where information that is newer, and harder to remember are shown more frequently, while information that is older and easier to remember is shown less frequently. This is done to take advantage of the spacing effect which can be a better way and quicker way to learn and keep information.
Many spaced repetition programs such as Anki have been made to help people to use spaced repetition but it is also possible to do this without software by using the Leitner system.
Implementations.
Software.
Items that are to be memorised are entered manually in a question and answer format. When it is time for the item to be learned, either the question or answer is displayed on screen (although it is possible to make it so only the question will be asked) and the user will try to answer it. After answering the user then tells the program how difficult the question was to answer. Depending on the difficulty the program will schedule when the user will see the question again.