The tower-like structure that houses most of the drilling controls. They are usually pyramidal in shape and offer a good strength-to-weight ratio. If the derrick design does not allow it to be moved easily in one piece, special ironworkers must assemble them piece by piece, and in some cases disassemble them if they are to be moved.

The phase of petroleum operations that occurs after exploration has proven successful, and before full-scale production. 

A well drilled in a proven field for the purpose of completing the desired spacing pattern of production.

The tool used to crush or cut rock. The bit is on the bottom of the drillstring and must be changed when it becomes excessively dull or stops making progress. Most bits work by scraping or crushing the rock, or both, usually as part of a rotational motion.

A drilling unit that is not permanently fixed to the seabed.

The drillpipe connects the rig surface equipment with the bottomhole assembly and the bit, both to pump drilling fluid to the bit and to be able to raise, lower and rotate the bottomhole assembly and bit.

A drip is a small vessel in a pipeline which receives water and heavy hydrocarbons that drop out of a gas stream. Drips are normally installed in the lower points of flow lines and must be blown periodically to remove liquids.

Dry gas is natural gas that is composed mainly of methane with only minor amounts of ethane, propane and butane and little or no heavier hydrocarbons in the gasoline range.