In the print industry and in bookbinding, the term fold describes a sharp break or bend in the paper. By folding the paper letters are, for example, prepared for enveloping. The folding is usually performed by folding machines. In preparation for folding folding marks are applied. Based on these marks the folding machines know where to fold the paper. There are two bacic types of folds: * Parallel folds: In parallel folding, all other folds are always parallel to the first one. Common examples of this are the z-fold, the gate fold, the letter fold, the double fold, or the double gate fold. * Right angle folds: In right angle folding, the next fold is always at a right angle to the previous one.