What is regular calculus?

I think by "regular calculus" it is meant simple derivatives and integrations. Regular calculus would be first year calculus probably not including multi-variable calculus or calculus of variations or vector calculus. Wikipedia gives a good explanation of calculus. If you want to sound smart, call it "The Calculus".

It is the study of the rate of change (how things change, in relation to other things, often time)

In most Universities, regular calculus are the standard analysis of Calculus, concentrating more on the application of it rather than the concept. in comparison is either called "advanced calculus" or in my U, "Honours Calculus" which takes analysis to a whole new level. Both first year course, but the advanced one concentrates on the understanding of concepts, theorems rather than applications alone. It comes in the form of "mathematical proof". Regular Calculus does proofs too, but not as often.

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Regular calculus is most probably calculus taught in high school or university level, which is simple, mostly single-variable calculus.

But then, there are also different calculi called non-Newtonian calculi. These are the non-standard, non-regular calculi, in which different operators are defined. For example, "regular calculus" might mean an additive calculus (where the integral is defined by adding up extremely small pieces), while an integral in multiplicative calculus might involve multiplying infinitely many pieces close to 1.