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 "dry-tight" 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.