Not a misspellling of calendar, the calender is a set of cylinders or rollers used to create a smooth texture on paper. Paper that is not run through the calenders is less smooth.
At the end of the papermaking process the paper is pressed between the calenders to give a smooth and uniform surface. The process is called calendering. Heated calenders create a smoother paper while cool calenders give it a very slight texture. Using an extra set of calenders — supercalenders produces a thinner and smoother paper called supercalendered paper.
Calenders are used not only on paper but also to create a flatter, smoother surface on some fabrics, polymers, and rubber.