In a hospital, a code is some kind of special or emergency situation that about which many people need to be notified. Typically the hospital intercom is used to broadcast the alert. You could hear something like "Code Green in the ER" should you ever visit a hospital. To "call a code" is to alert hospital staff that some emergent situation (aka "emergency") is occurring. While the exact colors* may vary, the following is a relatively standard list of codes one might exect to ever hear called while in a hospital. Codes Blue, Green, and Red are fairly standard. The rest may not be of concern to all hospitals.

It is interesting how a Code Blue is handled in different hospitals. Very large, urban hospitals tend to have a "crash team" on hand at all hours. This team's job is to respond to Code Blue emergencies. This team would typically be made up of two or three physicians (generally surgeons), and probably an anesthesiologist and a nurse or two. In smaller communities (and smaller hospitals), a Code Blue is a call to all available physicians in the hospital. This pretty much equates to anyone not already scrubbed in to the OR.

* Not all hospitals use colors; some use a numeric system. In that case, a Code Blue might equate to something like Code 99.