An in-depth look at what our favorite word to throw around actually means.
Anyone who has been behind the wheel of a BMW and a V-Tech Honda knows that two cars with similar horsepower outputs can feel drastically different. That has a bit more to do with how each engine is designed to deliver power, but for the most part, despite the differences, you can expect an engine with 600 horsepower to feel quite brisk compared to one with 150 horses. What you really should know is what the word "horsepower" actually means when a number isn't attached to it.
In technical terms, it's used to quantify the amount of work an engine can do. Bear in mind that work quantity is defined by how much mass an engine can move, how far it can move it, and how quickly it's moving it. And you would know from paying attention in science classes, there are more units in which that can be used to measure work ability that we'd like to count.
The reason horsepower became such a highly used metric to measure the amount of work an engine can do has to do with marketing. Prior to the age of the internal combustion engine, it was horses that did the vast majority of laborious physical work. When the internal combustion engine was invented and it came time to sell these power plants to industrialists, it was important to come up with a unit that was simple enough to allow them to understand how many horses the engine could essentially replace. And thus, the unit "horsepower" was born.