Head: The height of a column or body of fluid above a given point expressed in linear units. Head is often used to indicate gauge pressure. Pressure is equal to the height times the density of the fluid.

Heat: The form of energy that has the capacity to create warmth or to increase the temperature of a substance. Any energy that is wasted or used to overcome friction is converted to heat. Heat is measured in calories or British Thermal Units (BTU_s). One BTU is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

Heat Exchanger: A device which transfers heat through a conducting wall from one fluid to another.

Horsepower (HP): The power required to lift 550 pounds one foot in one second or 33,000 pounds one foot in minute. A horsepower is equal to 746 watts or to 42.4 British Thermal Unit per minute.

Holding Torque: Sometimes called static torque, it is specifies the maximum external force or torque or torque that can be applied to a stopped, energized motor without causing the rotor to rotate continuously.

Home: A reference position in a motion control system derived from a mechanical datum or switch. Often designated as the "zero" position.

Hydraulic Balance: A condition of equal opposed hydraulic forces acting within a hydraulic component.

Hydraulics: Engineering science pertaining to the energy of liquid flow and pressure.

Hydrostatics: Engineering science pertaining to the energy of confined fluid.

Hybrid Servo: A brushless servo motor based on a conventional hybrid stepper. It may use either a resolver or encoder for commutation feedback.

Hysteresis: The differences in response of a system to an increasing or a decreasing input signal.