Code-1, Code-2, Code-3 and Code-4 are examples of common police terminology, according to About.com. Code-1 refers to a non-emergency call, Code-2 refers to an urgent situation, and Code-3 means the situation requires lights and siren. Code-4 means the situation is under control and requires no further assistance.
Law enforcement officers use codes to communicate quickly. When police radio codes were devised in 1937, radios often failed to broadcast the first syllable of a transmission. Thus many police codes begin with a 10 or 11. Examples are 10-4, which means understood, and 11-14, which means animal bite, according to PoliceCodes.net.
Radio codes and police slang may differ from department to department, according to Police magazine.