The Haymow Shuffle is a card shuffle that is closely related to the Monge Shuffle.
The Haymow is done as follows:
The pack is held in the left hand. The left thumb pushes over a block of cards toward the right. The right hand takes this block. The left thumb pushes over another block, which is taken beneath the first. Another block is pushed over, and taken on top of the right hand's stock. Continue alternating, until all of the cards are in the right hand.
It's a rather primitive shuffle, that is still in use in many western countries, primarily among people with little experience handling cards. (Ironically, it actually does a better job of mixing than more sophisticated shuffles.)
The Charlier Shuffle is a false Haymow. It looks much the same, but the deck is not mixed; at the conclusion, the pack is not mixed; rather, it has simply been given a complete cut.
The Haymow is also equivalent of a shuffle named "Mélange au pouce (thumb shuffle)" or "Mélange paysan" (See Robert-Houdin for a Stack with this shuffle).
T.A. Waters in Encyclopedia of Magic and Magicians (1988) also says that in Britain the term Haymow Shuffle is "sometimes applied to a mixing procedure in which the cards are divided into two halves, spread slightly, and then pushed together to interleave in random fashion. This latter procedure is said to be the oldest known method commonly used for shuffling cards."