Fortunately, the MIT community still uses names when referring to the first two, but since students and faculty alike are very comfortable using numbers for the others, we will explain how these numbers work. Each class within a course is called a subject and is known by a two-part number. The part before the decimal specifies the course, and the part after the decimal gives some information about the nature of the subject. It may, indicate a level. Or it could indicate a particular sub-discipline.
Buildings have both names and numbers and are often known by the latter.
For example, the Daniel R. Guggenheim Building, which houses the Department of Aeronautics and Astronautics and is named for the philanthropist who supported the pioneers of manned flight, is Building 33. The Eastman Laboratories, named for George Eastman, founder of Eastman Kodak and donor of the funds that made it possible for MIT to build its present campus, is Building 6.