[Pseudoscience-is-malarkey (OP)]

Perhaps impossible, but give it your best shot, please.

[evan_au]

Historical answer: "calculus" originally comes from the Latin, and means a small stone or pebble. These were used in an abacus for calculations.

[Origin]

Perhaps impossible, but give it your best shot, please.

Type into google "calculus definition". 

You're welcome.

[alancalverd]

Most schools, at least in my day, taught differential calculus first, then moved on to integral calculus as an inverse problem. The Open University, again back in the mists of the 1970s, did it the other way around. I was mystified at first but it's actually a lot more intuitive.

If you draw a graph of, say the number of people of each age (on the vertical axis) against year of birth (horizontal) it's pretty obvious that the total number of people is equal to the area under the curve. Integral calculus is the process of calculating the area under a curve if we know the mathematical formula for that curve.

Differential calculus is the process of calculating the tangent  at any point on the curve. It is less obviously useful in the "population" case but if the tangent changed suddenly in, say, 1963 we'd have reason to believe that something significant happened around that time.

[Eternal Student]

Hi.

What is the real purpose for starting this thread?   Is it a social experiment to see how much time people will spend writing something?

   Anyway, I suppose we just get on and oblige.  You asked for a sentence or two.

Calculus is something quite simple and yet it has an inexplicable and unreasonable effectiveness.  It can be taught to school children and they can use it to solve a very large set of problems.

Best Wishes.

[alancalverd]

It's often fun to try to explain something you take for granted, for an entirely naive audience.

In this case you could summarise calculus as the mathematics of things that change, but I doubt that the audience would be any the wiser.

[paul cotter]

The analysis of functions of variability.

[Pseudoscience-is-malarkey (OP)]

Calculus is something quite simple and yet it has an inexplicable and unreasonable effectiveness.  It can be taught to school children and they can use it to solve a very large set of problems.

In this case you could summarise calculus as the mathematics of things that change, but I doubt that the audience would be any the wiser.

The analysis of functions of variability.

Isaac Azimov's inspiration for his Foundation saga was primarily two things: the collapse of the Roman Empire (At least Edward Gibbon's take on it) and calculus. The protagonist on Foundation uses math to predict the future. Interesting.

[Petrochemicals]

Historical answer: "calculus" originally comes from the Latin, and means a small stone or pebble. These were used in an abacus for calculations.

a hard substance that forms on the teeth:

The disease process begins when plaque on the tooth hardens to tartar, which hardens further to become calcified tartar, or calculus.

[paul cotter]

One could also have a renal calculus but I don't recommend it. Commonly called a kidney stone and reputed to be one of the most intense of pain syndromes known to man. I have some experience here, having been afflicted twice: one time it was indescribably bad and the second time more of a nagging pain. The strange thing about this pain is that it responds much better to a specific nsaid, diclofenac, than any opioid painkiller.

[Bored chemist]

How would you explain or define calculus in a sentence or two?
Badly, because it's complicated.

[alancalverd]

Not if you take the Open University approach (see #3 above). It begins almost intuitively and develops quite logically without introducing the infinitesimals that puzzle most beginners.

[Darlalarsen]

Perhaps impossible, but give it your best shot, please.

I remember my college professor saying it was practically impossible.
Besides I don't hesitate to give you this source https://supremestudy.com/ [nofollow] to try to reach out to these guys, because they deal with everything that has to do with college and school, most likely they could give you an answer to this question. Because I have used them several times and I have always been satisfied with what they have done, in any case it is possible to correct what you don't like.
This is all I know 

[alancalverd]

Try a better college next time. I'd worry about a professor teaching a subject he couldn't define - that's philosophy or theology, not proper education.

[remotemass]

Perhaps impossible, but give it your best shot, please.

It is not a sentence or two but I highly recommend you the book, "The Calculus Gallery – Masterpieces from Newton to Lebesgue", by William Dunham. It is a lovely and beautiful reading. Give it a go. It will not disappoint you.