Folding a printed piece horizontally at least twice, in the same vertical direction, thereby capturing the first fold in the second. The same effect is achieved by rolling the sheet horizontally into a tube shape and flattening the tube by creasing the two horizontal edges.

A bindery term used to describe a type of fold which uses two parallel folds to create three panels that allow a sheet of letterhead or other printed material to fit a business envelope. Also referred to as a barrel fold or wrap around fold.

Folding pattern in which the folds are parallel and in the same direction, so that a kind of spiral is produced. The letter fold is a parallel fold. Two or more panels of the same width of the folded signature are folded around one panel. When the signature is folded twice, there are three panels on each side (six pages); with a tri-fold, the result is four panels on each side (eight pages).