Reading to Entertain — The level of reading taught in our elementary schools.
Reading to Inform — A superficial read. You skim, dive in and out, and get a feel for the book and get the gist of things.
Reading to Understand — The real workhorse of reading. This is a thorough reading where you chew on things and digest them.
Reading to Master — If you just read one book on a topic odds are you have a lot of blind spots in your knowledge. Synoptical reading is reading a variety of books and articles on the same topic, finding and evaluating the contradictions, and forming an opinion.