According to dictionary.com, http://dictionary.reference.com/search?q=calculus Calculus is... a.The branch of mathematics that deals with limits and the differentiation and integration of functions of one or more variables. b.A method of analysis or calculation using a special symbolic notation. The combined mathematics of differential calculus and integral calculus.

Calculus is the study of rates of change. In short, you can find the instantaneous rate of change (i.e. "slope") of a function (differentiation). You can also use it to take sums of an infinite number of quantities and find the area under a curve (integration). All the rest are just applications.

As well as the mathematical meaning, "calculus" can also mead a mineral deposit in the body - plaque on the teeth, or a kidney stone, for example.

Calculus is the latin word for "pebble" or "little stone" 1) This word has been use in the medicine field, talking about some little stones which can be produced in various places in the body, for instance on teeth, or gall stone or kidney stone or urinary stones. 2) This word has also been used in mathematics, to design different kinds of calculation. The original use of the term for calculation came from the fact that people were using little stones to make their simple calculations a long time ago. The term "calculus" was later translated to "calculation". But to describe very particular kinds of higher calculations, people rather employed latin terms. Or they were just writing their works in latin at that time. So Leibniz used some terms such as "infinitesimal calculus" and "differential calculus" and "integral calculus" in his studies. The term "calculus" was adopted later in the English Language. In French we do not use the latin terms, but use "calcul" for "calculation" and "calcul infinitesimal" or "calcul différentiel" or "calcul intégral" for those things where Leibnitz has been working on. (Newton discovered these things also, independently) 3) References and further information: http://en.wikipedia.org/wiki/Calculus_%28disambiguation%29 http://en.wikipedia.org/wiki/Calculus http://en.wikipedia.org/wiki/Gottfried_Leibniz#Calculus http://en.wikipedia.org/wiki/Differential_calculus http://en.wikipedia.org/wiki/History_of_calculus

A small stone used for calculating. EDIT: I answered "what is THE calculus", which is a completely different question from this question to which the moderators have moved my answer. I reiterate my annoyance that the moderators move answers without reading the content of the answers, and thus move perfectly valid answers onto unrelated questions where the previously perfectly valid answer now sounds stupid.

Yeah, It's A Medical Term For Stone, So I Suppose It Means Stone In Greek Or Latin.