As an adjective, it means necessary and important as a part of a whole. In math, an integral is a calculation related to areas under curves and accumulation.
From Latin 'integralis' meaning 'whole, complete', from 'integer' (whole, untouched). The mathematical sense developed from the idea of restoring or summing up tiny parts into a whole.
When something is integral, you can’t remove it without breaking the whole—like a keystone in an arch. In calculus, integrals do the same thing with numbers: they rebuild a whole quantity from infinitely many tiny pieces.
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