According to MedicineNet, the term "code red" does not have a specific definition, but when a medical team issues a code in any color, it frequently means that a patient has had a heart attack. Each clinic or hospital is free to determine how it defines the various colors. Both code red and code blue frequently refer to a heart attack, but they also sometimes refer to terrorist threats, bomb threats, juvenile abductions or other significant emergencies. Because each facility is free to determine its own system, it is important to garner awareness before you start working at a new medical clinic.
The method that clinics use to announce emergencies varies as well. Some announce them as codes through the public address system, but others use pagers to send alerts only to the necessary medical personnel. Also, the term code also appears in institutions other than medical clinics and hospitals. Schools, government buildings and offices all sometimes use code references to alert staff that there is an emergency taking place.
The best way to make sure that you know what announcements such as code red mean is to ensure that you have all of the requisite training when entering a new facility.