A "code" as it was referred to above is short for Code Blue, the universal, my patient is crashing, call for help. It's announced overhead in the hospital and at bigger facilities to the code blue beepers.
In small hospitals, like the one I used to work at, an ICU nurse, respiratory therapist, ER doc, ER tech, nursing supervisor and security would respond.
In a big university hospital like I work at now, a code blue team will respond, which includes 2 ICU nurses, respiratory, a pharmacist, nursing supervisor, and the various residents from various services on the code team that day and then some.
Hope this helps.