9-1-1 or 911 (a lot of times said as "nine-one-one" or "nine-eleven") is the emergency telephone number for the United States, Canada, and Argentina. This number can only be used for real emergencies. In other words, you use it when you are in serious trouble. The use of the number when there is no emergency may end in a criminal charge.
9-1-1 Facts for Kids. Kiddle Encyclopedia.