An odometer is a device that measures and displays how far a vehicle has traveled. Look at the dashboard of a car and you'll see numbers showing the total miles or kilometers that car has driven since it was brand new. That's the odometer reading.

If a car's odometer reads 50,000 miles, that vehicle has covered enough distance to drive about twice around the Earth at the equator.

Odometers matter for several reasons. They help owners know when their car needs maintenance, like an oil change after a certain number of miles. They affect a vehicle's value: a car with 20,000 miles is worth more than one with 200,000 miles because it has more useful life left. That's why tampering with an odometer to make a car seem newer than it is counts as fraud and is illegal.

Many vehicles also have a trip odometer that can be reset to zero. This lets you measure specific journeys, like tracking how far you drove on a vacation or checking your gas mileage by seeing how many miles you traveled on one tank of fuel.