For example, when you read a text about George Washington, this is passive review.
If you answer a question "Who was the first US President?", this is active recall.
Active recall is many times more efficient in consolidating long-term memory. This is why just reading your study notes before exam is not likely to leave a long-lasting memory trace. On the other hand, if you ask your colleague to test you on the same material, the results will be better in the long run.