The Origin of some Oilfield terms is unclear but this colorful Industry has its own colorful language that can be confusing to an outsider. Here are a few of them from the Drilling & Production side of the Industry. This is by no means an all inclusive list of Oil Well Drilling terms, just some of the most colorful.
Terms Commonly Used In The Oil & Gas Well Drilling & Production
Bell Nipple: An enlarged pipe at the top of a casing string that serves as a funnel to guide drilling tools into   the top of a well.

Blowout: An uncontrolled release of underground pressure which can cost loss of life and property. A “wild well” is a blowout that is ablaze and has not been extinguished.

Cat Line: A relatively smaller cable used with other equipment to move small rig/tools and drillstring components and to provide tension on the tongs for tightening or loosening threaded connections.

Catwalk: A long, rectangular platform about 3 ft [0.9 m] high, usually made of steel and located perpendicular to the vee-door at the bottom of the slide. This platform is used as a staging area for rig and drillstring tools, components that are about to be picked up and run, or components that have been run and are being laid down.

Doodlebugger: A seismic company employee conducting/performing seismic surveys in the field.

Doghouse: Enclosure usually on the rig floor where the crew can shelter from the weather.

Elevator: A hinged mechanism that may be closed around drill pipe or other drill string components to facilitate lowering them into the wellbore or lifting them out of the wellbore.

Frac Job: Operation that involves large pumps that force water or other fluids down the casing and out into the formation fracturing it, so oil or gas can be released.

Fish: Any object that has been dropped or lost down the hole.

Flare: Device located away from the drilling rig used to burn off gas that has been encounted and is flowing up the wellbore, also the act of burning the gas.

Fishing: The act of using specialized tools lowered down hole on the drill string to retrieve a fish.

Gas Buster: A simple separator vessel used to remove free or entrained gas from fluids circulated in the wellbore, such as mud used during drilling operations.

Gun Barrel: A settling tank used for treating oil. Oil and brine are separated only by gravity segregation forces. The clean oil floats to the top and brine is removed from the bottom of the tank. Gun barrels are found predominantly in older or marginal fields. A gun barrel is also called a wash tank.
Hand: A rig worker or service hand that passed the “worm” stage and can work unsupervised.

Intelligent Well: An oil or gas well equipped with monitoring equipment and completion components that can be adjusted to optimize production, either automatically or with some operator intervention.

JackUp Rig:  A self-contained combination drilling rig and floating barge, fitted with long support legs that can be raised or lowered independently of each other.

Joint: A length of drill pipe.

Kick: An intrusion of pressurized gas into the wellbore that causes drilling fluid to be displaced. Can be the prelude to a blowout.

Kill: To stop a well from flowing or having the ability to flow into the wellbore. Kill procedures typically involve circulating reservoir fluids out of the wellbore or pumping higher density mud into the wellbore, or both.

Knowledge Box: Metal box in the doghouse containing the drilling report, pipe tally and other important papers.

Liner: A casing string that does not extend to the top of the wellbore, but instead is anchored or suspended from inside the bottom of the previous casing string.

Monkeyboard: The small platform about midway up the derrick where the derrickman stands/works and racks pipe.

Mud: A term that is generally synonymous with drilling fluid and that encompasses most fluids used in hydrocarbon drilling operations, especially fluids that contain significant amounts of suspended solids, emulsified water or oil.

Mud Man: A drilling fluids technician responsible for formulating drilling mud or fluid.

Mud Logger: A service hand working for a Mud Logging company, often a geologist, that checks the cuttings from the drill bit for type of rock and traces of oil or gas and checks for concentrations of hydrocarbons in the drilling mud and notes these on a log, which is like a foot by foot road map of the drilled well.

Nipple Up:  To put together, connect parts and plumbing, or otherwise make ready for use. This term is usually reserved for the installation of a BOP or blowout preventer stack

Oil:  A simple or complex liquid mixture of hydrocarbons that can be refined to yield gasoline, kerosene, diesel fuel, and various other products.

Overshot: A downhole tool used in fishing operations to engage on the outside surface of a pipe or tool. A grapple, or similar slip mechanism, on the overshot grips the fish, allowing application of tensile force and jarring action. If the fish cannot be removed, a release system within the overshot allows the overshot to be disengaged and retrieved.

Pig: A device with blades or brushes inserted into a pipeline or cleaning for cleaning purposes. The pressure of the oil or gas behind pushes the pig along to clean out rust, wax, scale and debris.

Packer: A device used to seal off a certain part of the casing or wellbore in order to pump cement, etc. into a certain zone.

Pill:  Often a concoction of fibers and special chemicals and polymers that is pumped down hole to stop drilling fluid from leaking into the formation being drilled.

Possum Belly: Mud tank or pit closest to the return line where drilling fluid is returned from down hole.

Pusher: The location supervisor for the drilling contractor. The tool pusher is usually a senior, experienced individual who has worked his way up through the ranks of the drilling crew positions. His job is largely administrative, including ensuring that the rig has sufficient materials, spare parts and skilled personnel to continue efficient operations. The tool pusher also serves as a trusted advisor to many personnel on the rig site, including the operator's representative, the company man.

Pooh: Abbreviation for “Pull Out Of Hole” or to Trip Out.

Roustabout: Any unskilled manual laborer on the rigsite. A roustabout may be part of the drilling contractor's employee workforce, or may be on location temporarily for special operations. Roustabouts are commonly hired to ensure that the skilled personnel that run an expensive drilling rig are not distracted by peripheral tasks, ranging from cleaning up location to cleaning threads to digging trenches to scraping and painting rig components.

Short Trip: An abbreviated recovery of pipe out of, and then the replacement of same back into the wellbore. May involve pulling ten or more stands but not all of the pipe that extends to the bottom of the hole.

Show: The presence of oil or gas at a certain depth as indicated by gas or fluid coming up with the mud. Can indicate the well is productive.

Trip: Pulling all the drill pipe out of the hole or running pipe into the hole. Done when bits are changed, mud motors, etc. are changed, casing liners are added, or when the well is done or needs to be logged with a wire line unit.

Underbalanced: Situation where the drilling “mud” or fluid is not sufficient to hold back underground pressure that may be encountered.

Vee Door: The upside down V-shaped opening in one side of the derrick that enables long pipes and tools to be lifted into the interior of the rig/derrick. This opening is aligned with the slide and catwalk of the rig. “Worms” or Rookies are often tricked by being told to “go find the key to the V-Door”. Since none exist, it is loads of fun for the broke out hands.

Weight Up: To add weight, typically by adding barite to the drilling mud.

Wells: The place where a well is drilled. Also called well site. The hole made by the drilling bit, which can be open, cased, or both. Also called borehole, hole, or wellbore.

Worm: A new, completely inexperienced oilfield worker that is not yet a “Hand”. Worm’s may be required to wear orange hard hats or stickers that say “New On Job”.

Zip Collars: Drill collars (usually straight drill collars) that have been machined with a reduced diameter at the box (up) end so that they may be more easily handled with open-and-close elevators.