Passive learning is knowledge that you pick up without even trying, by just paying attention. Like learning the cast of your favorite TV show, or the lyrics to your favorite song. It tends to fade quickly without repetition or reinforcement, but we are doing it constantly, like a whale straining plankton, often without even realizing it.
Active learning is learning with a purpose. It is driven by curiosity and interest, and usually leads somewhere. This mode of learning is more like a squirrel gathering nuts.
Both are useful, both are going on all the time, but active learning is the kind that tends to lead to improvement (of oneself and the world).