A tachometer is an instrument used to measure the rotational speed of an object, typically in revolutions per minute (RPM). It is commonly found in vehicles, where it helps drivers monitor the engine's performance and avoid over-revving, which can cause damage. Tachometers can be analog, featuring a dial and needle, or digital, displaying the speed on a screen. They are essential in various applications, including automobiles, motorcycles, and aircraft, providing crucial information for efficient operation and maintenance.