Signal
A signal as referred to in communication systems, signal processing, and electrical engineering is a function that "conveys information about the behavior or attributes of some phenomenon". In the physical world, any quantity exhibiting variation in time or variation in space (such as an image) is potentially a signal that might provide information on the status of a physical system, or convey a message between observers, among other possibilities. The IEEE Transactions on Signal Processing states that the term "signal" includes audio, video, speech, image, communication, geophysical, sonar, radar, medical and musical signals.
Integration
I see with much pleasure that you are working on a large work on the integral Calculus [ … ] The reconciliation of the methods which you are planning to make, serves to clarify them mutually, and what they have in common contains very often their true metaphysics; this is why that metaphysics is almost the last thing that one discovers. The spirit arrives at the results as if by instinct; it is only on reflecting upon the route that it and others have followed that it succeeds in generalising the methods and in discovering its metaphysics.
Pierre-Simon Laplace (1792) in: I. Grattan-Guinness Convolutions in French Mathematics, 1800-1840:From the Calculus and Mechanics to Mathematical Analysis and Mathematical Physics. Vol.1: The Setting, Springer Science & Business Media, 1 July 1990, p. 139.
Integration
The formation of the differential equations proper to the phenomena is, independent of their integration, a very important acquisition, on account of the approximations which mathematical analysis allows between questions, otherwise heterogeneous.
Auguste Comte in: The Positive Philosophy of Auguste Comte, Volume 1, Trübner, 1875, p. 213.
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