Wikipedia logo The Simple English Wikipedia has an article on: Calculus Pronunciation (UK) IPA (key): /ˈkæl.kjʊ.ləs/ (US) IPA (key): /ˈkæl.kjə.ləs/ Audio (US)(file) Hyphenation: en‧cal‧cu‧lus Noun Singular calculus Plural calculi or calculuses (uncountable) Calculus is a branch of mathematics that involves understanding mathematical functions. One use of calculus is for finding rates of change and maximization. Wikiwand - on Seamless Wikipedia browsing. On steroids.