Jill decides to study for her biology final exam by studying for 20 minutes each day for the next three weeks, as opposed to studying all the material at once. which study technique is she using?

Jill is using a technique known as Spaced Repetition. In this technique, the learner studies in short periods with great frequency over a long period of time, frequently testing herself along the way. This aids in long-term retention for the learner. 

The opposite of this technique would be cramming, also known as block learning. Spaced Repetition is widely accepted as the superior study technique.