Recency effect
The recency effect is the way you remember the last few things in a list best, because they are still fresh in your short-term memory when you try to recall them. It is the partner of the primacy effect, which boosts the first few items.
When you read a list of facts or hear a lecture, the items at the end stick around in your head for a short while. So if you test yourself right away, those last points come back easily. The catch is that this boost fades fast. Wait a few minutes, or do something else in between, and the end of the list is no longer special.
This matters for how you study. The middle of a long session is the danger zone, since it gets neither the fresh boost of the end nor the extra attention the start often gets. Breaking your material into smaller chunks gives you more starts and more ends, so fewer things fall into that weak middle.
It also explains a common trap. The topic you reviewed last feels the most solid, but that feeling is just recency, not real learning. The fix is to come back to that material later, when the short-term boost is gone, and see if it still holds.
Mia crams a list of twenty key terms the night before her biology test. The next morning she only remembers the last five clearly, because the rest had nothing keeping them fresh. After that she starts reviewing in small batches and quizzing herself a day later, not right away.