The process in which corrugated board, commonly (and mistakenly) known as cardboard, is made. This process involves a large machine appropriately named a corrugator, a secret mix of starches and paper.
The finished product of this process is a rigid board of paper that has flat peices of paper on the top and bottom called the liner and a wavy or fluted peice of paper between them called the medium. An imaginative person (though there aren't many in the corrugating industry) could think of it as a paper sandwich. The liners are like the bread and the meduim is like your favorite condiment. Following the sandwich analogy, the layers can be stacked to make a board which has two and even three mediums.
The method was created by a guy named Albert Jones in 1871, but wasn't widely used to make boxes and other box-like things until the early 1900's.