What is "spaced repetition" and how can I use it to improve my chess? What is spaced repetition?

How can I apply it to studying and improving my chess?

Is it just for tactics or can I also use it for openings and endgames?

What experience do people have with it and with what results?
Spaced repetition is a learning technique that repeats content after increasing time spans according to learning success, i.e. faster for stuff you haven't grasped yet, longer if you do well.

In chess this is either used to learn a certain set of (easy) tactical exercises basically by heart ("woodpecker method" according to Axel Smith, Michael de la Maza, …), which is supposed to improve your tactical pattern recognition.

Or it is used to learn your opening repertoire by heart. For example by using the software Chess Position Trainer.

In my experience both are probably beneficial, but I cannot offer more than anecdotal evidence. Also you should complement it with exercises that tax more than your memory.