knots, miles per hour, mph, kilometers per hour, kph, etc.
Speed is a measure of how quickly an object is moving. It is given in units of distance divided by time. Velocity, in addition to telling us how fast something is moving, also tells which direction it is travelling.
The SI unit of speed is the meter per second, but kilometers per hour or miles per hour are more commonly used. Also, for air or marine travel, the unit knot (nautical miles per hour) is often used.
The speed of light in a vacuum is 299,792,458 meters per second. According to the theory of special relativity, this is the fastest speed at which energy or information can travel.