Shopping period lasts for the first two weeks of the semester, and during shopping, pretty much everyone tries out a ton of classes that they’re interested in taking. Upperclassmen normally have 1-3 concentration requirements per semester, but almost everyone can take at least one class purely out of interest most semesters. Most people attend LOTS of classes for the first two days of classes, I’d say 7-10 is normal. People are literally running across campus trying to be in two places at once. By the end of the first week, you can normally narrow down below 7. For the next week and a half, you can try out the classes still, but they start with some light assignment. After two weeks, most people choose to take 4 classes, but 3 and 5 are also considered full-time.
Every class at Brown can be taken Satisfactory/No Credit, which is our version of pass fail. Some are required to be S/NC–literary arts, visual art, and intro physics come to mind. The point of the S/NC option is to promote exploration in new fields that people might not be as comfortable. For example, as a very science-y concentrator, I took a journalism class S/NC so that I could purely learn the material and techniques without worrying about grades. Auditing a course means something different for every class, but generally means attending class and doing the readings but no assignments. It’s a fantastic way to learn new things, and pretty common–Brown is THE place for academically curious people. Plus auditing shows up on your transcript, which is fun.
Normal courseload is 4 classes every semester, with one S/NC. TAships, research, and music stuff often can count as course credit and lots of people use them as a 4.5/5th course. Crazy people (me among them this semester) take five classes, and a five class schedule almost always includes S/NC in at least one class.