10-1-1. EMERGENCY DETERMINATIONS
a. An emergency can be either a Distress or an Urgency condition as defined in the "Pilot/Controller Glossary."
b. A pilot who encounters a Distress condition should declare an emergency by beginning the initial communication with the word "Mayday," preferably repeated three times. For an Urgency condition, the word "Pan-Pan" should be used in the same manner.
c. If the words "Mayday" or "Pan-Pan" are not used and you are in doubt that a situation constitutes an emergency or potential emergency, handle it as though it were an emergency.
d. Because of the infinite variety of possible emergency situations, specific procedures cannot be prescribed. However, when you believe an emergency exists or is imminent, select and pursue a course of action which appears to be most appropriate under the circumstances and which most nearly conforms to the instructions in this manual.
The above is from the FAA ATC handbook 7110.65.
Hope this helps to clear up any misunderstanding of ICAO vs FAA. What this means is that if the word emergemcy is heard, or thought to be heard it is to be considered the same as a Mayday call.