Because the centrifugal force exists only in rotating reference frames, but not in inertial reference frames, it's sometimes called a "fictitious" or "pseudo" force.

We don't like this characterization because there is nothing fictitious or pseudo about it when your car goes off the road and crashes, or when your bicycle skids out from under you when cornering a slippery curve. The Earth's equatorial bulge is not a fiction, nor is the problem an engineer confronts when designing turbine blades of jet engines that have to stay together at rotation rates of up to 100,000 revolutions per minute.