the ratio of the distance traveled (in miles) to the time spent traveling (in hours)
"The car's average speed was 60 mph, meaning it covered exactly sixty miles in one hour without stopping."
a speedometer reading for the momentary rate of travel
"The car's speedometer flickered to 70 mph as I merged onto the highway, confirming my sudden burst of acceleration."
Initialism of mile(s) per hour.
"The car accelerated from zero to sixty mph in just six seconds."
Mph is an abbreviation derived from the Greek miles (mile) and Latin per hora (per hour), originally used to denote miles per hour in speed measurements. It entered common usage as a standardized unit symbol rather than evolving through natural language change.