Why do we use the word Horsepower?

We use the word "horsepower" because it originated as a way to compare the power output of steam engines to the power of horses, which were the primary source of mechanical power at the time. James Watt, a key figure in the development of the steam engine, developed the unit to help market his engines. He calculated how much work a strong horse could do in a minute and used that as a benchmark for the power of his steam engines, making it easier for potential buyers to understand their capabilities relative to something familiar.