A process at the end of cotton cloth manufacture that produces a smooth surface texture with a slight sheen. The woven cloth is pulled through very hot rollers that polish its surface. Until the middle of the 20thC, and certainly for formal wear, most shirt collars were made separately and buttoned onto the shirt.
These collars were carefully laundered and calendered at home using a very hot, solid iron.
Batiste, cambric, glazed coton, glazed chintz are all calendared.