integral calculus

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The study of integration and its uses, such as in finding volumes, areas, and solutions of differential equations.

Wiktionary

1. n. calculus The calculus that generalizes summation to find areas, masses, volumes, sums, and totals of quantities described by continuously varying functions.

GNU Webster's 1913

1. n. a method which in the reverse of the differential, the primary object of which is to learn from the known ratio of the indefinitely small changes of two or more magnitudes, the relation of the magnitudes themselves, or, in other words, from having the differential of an algebraic expression to find the expression itself.
2. adj. See under Calculus.

WordNet 3.0

1. n. the part of calculus that deals with integration and its application in the solution of differential equations and in determining areas or volumes etc.