An odometer is the counter in a vehicle that tells you how far it has already gone, in miles or kilometres. In a car it is the number that keeps climbing. Many cars also have a trip odometer, a second counter you can set back to zero for one journey. It measures distance, not speed — that other dial, the one that jumps when you go faster, is the speedometer. Though actually, learners mix those two up all the time, and even some English speakers are sloppy about the names. The word is everyday in American English. British speakers often say mileage, or milometer, though odometer is understood and is normal in technical talk. People sometimes stretch it to any little device that counts how far you have walked or ridden, but the home of the word is still the dashboard. In older cars it was rolling numbers; now it is often a number on a screen. When someone secretly turns the number back on a used car to make it look newer, they are tampering with the odometer — that is dishonest, and in many places it is against the law. It is a plain, practical noun, not slang and not fancy.