A fob is a proximity access card. Fob supposedly stands for "For Opening Buildings." Its existence is the embodiment (or not) of a grammatical nightmare.
Fobs were introduced to Lancaster in 03.1 as a replacement for the outside door key after problems in previous years, wherein an individual losing a door key would require replacing everybody's outside door key. As of 2005, fobs are also used at JHU.
At Lancaster, fobs take the form of grey plastic objects vaguely resembling a USB flash drive (although they lack any external connections port). They make annoying beeping sounds when used to open doors, and work from much closer than is convenient for one's neck. Some students, however, very much enjoy using their fobs to open the doors, sometimes resulting in mock fights as to who gets to open a door first. They are not needed to open the main door of Thomas Hall, since Thomas houses the main offices and health office and as such is usually open. However, the side door does require a fob.
"Fob" is commonly used as a replacement for *poke* in the Lalala Game as well as for more nefarious words; the word can also be used as a euphemism for swear words (e.g., "Fob you!"). It is also used as a body part in the Hokey Pokey during Lancaster's Afterdance; during any Afterdances after key and fob return, "no-fob" or "lanyard" are used instead. When a camper suggested calling it a "Bob" because of its possibly offensive second definition, it was taken in by a few RAs who afterwards told their students to call it a "Bob" as well.