Traditionally, a cooper is someone who makes wooden staved vessels of a conical form, of greater length than breadth, bound together with hoops and possessing flat ends or heads. Examples of a cooper's work include but are not limited to casks, barrels, buckets, tubs, butter churns, hogsheads, firkins, tierces, rundlets, puncheons, pipes, tuns, butts, pins, and breakers. The word is derived from Middle Dutch kūpe, "basket, wood, tub" and may ultimately stem from cupa, the Latin word for vat Everything a cooper produces is referred to collectively as cooperage. "Cask" is a generic term used to describe any piece of cooperage containing a bouge, bilge, or bulge in the middle of the container. A barrel is technically a measure of the size of a cask, so the term "barrel-maker" cannot be used synonymously with "cooper." The facility in which casks are made is also referred to as a cooperage. Traditionally there were four divisions in the cooper's craft. The "dry" or "slack" cooper made containers that would be used to ship dry goods such as cereals, nails, tobacco, fruits and vegetables. The "drytight" cooper made casks designed to keep dry goods in and moisture out. Gunpowder and flour casks are examples of a "drytight" cooper's work. The "white cooper" made straight staved containers like washtubs, buckets and butter churns, that would hold water and other liquids, but did not allow shipping of the liquids. Usually there was no bending of wood involved in white cooperage. The "wet" or "tight" cooper made casks for long term storage and transportation of liquids that could even be under pressure, as with beer.
Sometimes—in more modern times—the profession of the cooper is specific to wineries, where the cooper would look after the aging barrels in which the wine is stored. While plastics, stainless steel, pallets, and corrugated cardboard have replaced most wooden containers and largely made the cooper obsolete, there is still demand for high quality wooden barrels, and it is thought that the highest quality barrels are those hand-made by professional coopers. Examples may be seen in the cooperage at Seguin Moreau, a cooperage which was incorporated into the House of Rémy in 1971 for the express purposes of providing barrels made of Limousin oak. Limousin oak is renowned for the rich vanilla-like flavor it imparts to cognac. Rémy Martin will then produce Rémy Martin Grand Cru in these barrels with a retail cost well in excess of USD $1500 per bottle. Therefore, a single barrel may be expected to hold nearly a quarter million dollars worth of cognac, thus providing an insight into the value of a professional cooper.
Sometimes, rarely today, coffin-makers are known as coopers.