Horsepower is a unit that measures how much work an engine or motor can do. When someone says a car has 300 horsepower, they're describing how powerful its engine is, how quickly it can accelerate, and how much it can pull or carry.

The term comes from the 1700s, when Scottish engineer James Watt needed a way to explain how powerful his new steam engines were. Since most people used horses to do heavy work like pulling plows or turning mill wheels, Watt measured how much work a typical horse could do in a given time. He calculated that one horsepower was the ability to lift 550 pounds one foot in one second. That became the standard.

Today we use horsepower to compare all kinds of engines and motors. A lawn mower might have 5 horsepower, while a sports car might have 500. More horsepower generally means more speed and pulling power, though it's not the only thing that matters. A tractor might have less horsepower than a race car but be better at pulling heavy loads because it's designed differently.