Hopper refers to a device for temporarily storing dust collected by an air pollution control device.

Hardware pertains to the physical components of a computer system such as the central processing unit (CPU), memory, disk storage, tape drives, plotters, printers, terminals, digitizers etc.

Hoist refers to a suspended machinery unit that is used for lifting and lowering a freely suspended (unguided) load; can be powered by hand, air or electricity; lifting medium either chain, wire rope or roller chain.

Hand-operated is described as requiring hand manipulation for operation ; not automatic or machine-driven; as, a hand-operated winch. The term hand operated is the opposite of automatic or powered. Examples of hand operated machines, devices or equipments are: arbor press which is a hand-operated machine tool, hand-operated grinder to grind meats used by chefs and cooks

Hydrogen peroxide is described as a valuable non-irritating and non-poisonous antiseptic. It effervesces in the presence of pus due to the liberation of oxygen. Usual strength 10 volumes, i.e. it contains ten times its volume of available oxygen.

Heat pump (as used in geothermal industry) in which the refrigerant exchanges heat in a heat exchanger with a fluid circulating through an earth connection medium - ground or ground water. The fluid is contained in a variety of loop/pipes configurations depending on the temperature of the ground and the ground area available. Loops may be installed horizontally or vertically in the ground or submersed in a body of water.

Hand control is described as a mechanical system that allows for operation of both the gas and brake pedals by either hand and is accomplished by means of a combination lever mounted to the steering column.

Hairspring is defined ad a fine spiral spring that regulates the movement of the balance wheel in a timepiece. Also known as balance spring, this is the small spiral spring that is attached to the balance wheel, the quality of which can affect the regularity and accuracy of a movement.