HDD (Horizontal Directional Drilling): A trenchless method of installing pipes, conduits, and cables underground by drilling a pilot bore, reaming, and then pulling the product pipe through.

Hydrostatic Pressure: The pressure exerted by a column of fluid, such as drilling mud, in the borehole.

Kelly: A square or hexagonal pipe that passes through the rotary table and transmits torque to the drill string, allowing for vertical movement while rotating. (Less common in modern top-drive rigs).

Kelly Bushing: A device that fits into the rotary table and transmits the rotational motion of the rotary table to the Kelly bar.

Lost Circulation: The loss of drilling fluid into fractured or permeable formations, resulting in a reduction or complete loss of fluid returns to the surface.

Logging (Well Logging): the practice of recording a detailed, continuous profile of subsurface rock formations penetrated by a borehole. Geoscientists can evaluate the geological composition, rock porosity, permeability, and the types of fluids present.

Mud: Drilling mud (or drilling fluid) is an engineered mixture of water, clay (like bentonite), and specialized polymers.

Mud Pit: A pit or tank used to store and condition drilling fluid.

Perforation: Holes punched through casing and cement into the surrounding formation to allow reservoir fluids to flow into the wellbore. (More common in oil/gas drilling than water well drilling).

Pilot Hole: A small-diameter borehole drilled initially to establish the path for a larger borehole.

Pore Pressure: The pressure exerted by fluids trapped within the pore spaces of subsurface rocks. 

Pump: Equipment used to circulate drilling fluid.

Reamer: A tool used to enlarge a pilot hole to a larger diameter.

Rig: A heavy-duty, integrated machine system used to bore deep holes into the earth for water, minerals, or energy

Rotary Drilling: A drilling method that involves rotating a drill bit to cut and crush rock.

Rotary Table: A rotating platform on the drill floor that provides torque to the kelly and drill string.

Spud In: The act of beginning to drill a new borehole.

Standpipe: A vertical pipe on the drilling rig that carries drilling fluid from the mud pumps to the swivel.

Stabilizer: A tool in the BHA that helps to keep the drill string centered in the borehole and reduce vibration.

Surface Casing: The first string of casing set in a well, used to protect shallow freshwater aquifers and provide structural integrity for subsequent drilling.

Swivel: A device that hangs from the drilling hook and supports the drill string, allowing it to rotate while the hose supplying drilling fluid remains stationary.

Top Drive: A motorized device located at the top of the mast that directly rotates the drill string, eliminating the need for a Kelly and rotary table. Modern rigs often use top drives.

Total Depth (TD): The maximum depth reached in a borehole.

Wellbore:  Is the actual excavated hole or pathway drilled into the earth to access subsurface resources.

Wellhead: The equipment installed at the surface of a wellbore that provides the interface for controlling and monitoring the well.

Weight on Bit (WOB): The downward force applied to the drill bit, crucial for effective drilling.