The American Heritage Dictionary calls the word "cop" "informal." That is, it's not slang, it's acceptable, but because it is informal it is less respectful than "policeman." Anything official or formal would use the word "police." For safety, a non-native speaker should avoid using the word "cop." Also... in the United States, due to concerns about gender neutrality, there is a trend to use the phrase "police officer" rather than the traditional word "policeman." Cops call cops "cops," I call cops "cops" when talking to friends, but if I were talking to a police officer I would use the word "police." If an elementary school had a police officer visit to talk about safety, the teacher would DEFINITELY introduce him to the children as "a police officer," not a "cop." I can imagine the local selectmen saying, before a meeting, "I see the cops have their new station on the agenda again," but then during the meeting saying "The next item concerns a request from the Chief of Police for funds to construct a new police station in District 23." Once--before the days of cell phones--my wife and I were walking and were stopped by an agitated man, pointing to a car, who said "There's been an accident. I need to stay here. Call an ambulance. Call the cops." Many Americans over forty remember a famous TV drama series called "Dragnet," about the Los Angeles Police Deparment, and it always opened: Announcer: The story you are about to hear... is true. Only the names have been changed, to protect the innocent. Joe: This... is The City. Los Angeles, California. I work here. I'm a cop.

Cop is the abbreviation of "constable on petrol".

Cop is slang for policeman. It's used regularly where I'm from. A police officer would say, "I'm a cop."

I've heard that difference. Cops is slang for Police Officers. It is very rude to call the Police Officer cops.