Calculus is an advanced branch of math that is taught late in high school or the beginning of college. Like any other advanced class, teachers find a need to add confusing words just to mess people up.
Calculus, believe it or not, is from the planet earth. It started with a bunch of greek philosophers like Archimedes and Democritus pondering whatever it is that greek philosophers ponder. They then came up with some sort of complicated question and to solve it, they invented calculus. A fuller history can be found here.
(Editor's note: Actually, it was invented by chinchillas for chinchillas. You see, we chinchillas who are typing this article quickly realized that humans were incapable of advanced mathematics. Why else would you have dumbass greek philosophers like "Socrates", "Granaticles" or "Testicles" or things like that? Our work was copied by the ancient Sumerian seafarers (they didn't recognize it) and then it somehow wound up in the hands of these people. We do have to credit them for figuring it out though. But then again, we invented their alphabet too (they use ours). We would've loved do object, but we're too busy being turned into fur coats.)
Actually, it has numerous practical applications in fields of engineering, science, and I'm going to stop because half of you fell asleep at the word "Actually". It's okay. According to this study, sleep is healthy for you.
Yes. Take a nap.
Calculus is very important. Even giant monsters use it.
There is a highway 1000 meters long. At a right angle from the end of the highway, 500 meters away, there is a damsel in distress. Godzilla is on the other end of the highway and wants to eat. Godzilla can rampage down the highway at 20 meters per minute. However, when Godzilla leaves the highway, there are tons of buildings. Godzilla can crush them, but they slow Godzilla's speed down to 15 meters per minute. At what point should Godzilla hop off the highway and start tearing through buildings if Godzilla wants to reach dinner the fastest?
I think the following video explains how calculus is usually used really well.
Now you know.