What is the difference between horsepower and torque?

Torque is rotational force, measured in pound-feet, and it describes how hard the engine can twist the crankshaft at a given moment. Horsepower is a rate, how much work is done per unit of time, and it is derived directly from torque and engine speed, roughly torque multiplied by rpm divided by a constant. Because horsepower is calculated from torque, the two are not independent quantities, which is why the popular framing of choosing between them is somewhat false. The commonly cited line is that torque gets you moving and horsepower keeps you going.

The practical differences show up in how vehicles feel and what they do well. Diesel engines and large-displacement engines produce high torque at low rpm, which is why they excel at towing, hauling, and delivering the shove you feel from a standstill. High-revving gasoline engines, common in sports cars and motorcycles, make their peak power at high rpm, which produces less low-end grunt but more speed at the top end. Electric motors changed the conversation entirely by delivering essentially full torque from zero rpm, which is why even modest electric cars feel startlingly quick off the line. Gearing matters as much as either figure, since transmissions multiply torque, which is exactly why a semi-truck with a few hundred horsepower can move eighty thousand pounds while a sports car with the same figure cannot.