At MIT, many things are known by numbers, initials or acronyms. Buildings and academic majors are known by numbers, so for instance Biology is Course 7. Some departments are known as EECS, BE, or BCS. You might take the T to work, see your AO in the morning, help train a UROP, walk down the Infinite Corridor, stop by OSP to drop off your fellowship application, go to COEUS and EHS training, meet with your PI, plan an IAP activity, buy a book at the Coop, and see a hack on the dome. A complete listing, with definitions of these and more acronyms and abbreviations, can be found at MIT Acronyms.