Speed tells you how fast something is moving; velocity tells you how fast and in what direction. A memory hook: a car's speedometer only shows speed, a single number, while velocity would need an arrow on a map to show which way it is heading too.
The core difference
Speed is simply a rate of movement, while velocity combines that rate with a direction.
- speed — how fast something moves, or the rate at which something happens: The train reached a top speed of 200 miles per hour.
- velocity — speed combined with direction: The rocket reached a velocity of over 7 kilometres per second.
How to tell them apart
Velocity comes from the Latin velox, meaning fast, by way of French. Speed has an older, gentler history: it comes from an Old English word meaning success or prosperity, the sense still faintly visible in the old phrase "Godspeed". The "fast movement" meaning developed later.
In everyday speech, people use speed and velocity interchangeably, and that is usually fine. The distinction matters mainly in physics and engineering, where direction changes the maths, and in economics, where velocity has its own specialised meaning describing how often money changes hands over a period of time.
