Like almost any automotive publication, we use the term "horsepower" all the time. It's one of those words that seems so straightforward. What is horsepower? Why, it's the power of a horse! What does that mean? Physical power? Political? Sexual? What horse? How is it measured? Let's find out, with pictures!
Like almost all our units of measurement, horsepower is an arbitrary set of criteria used so we can have some sort of reference for an abstract yet quantifiable thing, power. The term came around right about when you'd guess, the first time in history people had something to use other than an animal for power.
That thing was a steam engine, and James Watt was an early builder of such engines, and needed to sell them to people used to making horses do all the grunt work. Hence, the horse reference. If all this had been happening in Mongolia instead of the UK, we'd all be excited about how the engine in the new RS7 has 560 yakpower.
Anyway, I made a little infographic to try and show exactly what it is we're talking about when we talk about horsepower. I hope it helps!
Click "expand" to see it at full size, or click here.
(Sources: How Stuff Works, Wikipedia)
What Exactly Is Horsepower, Anyway?