A threaded pipe is a pipe

Pipe (material)

A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases , slurries, powders, masses of small solids...

 with screw-threaded

Screw thread

A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...

 ends for assembly.
The threaded pipes used in some plumbing installations for the delivery of gases or fluids under pressure have a threaded section that is slightly conical

Cone (geometry)

A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...

 (in contrast to the cylindrical section commonly found on bolts

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

 and leadscrew

Leadscrew

A leadscrew , also known as a power screw or translation screw, is a screw designed to translate turning motion into linear motion...

s). This is called a "tapered thread". The seal provided by a threaded pipe joint depends upon the labyrinth seal

Labyrinth seal

A labyrinth seal is a type of mechanical seal that provides a tortuous path to help prevent leakage. An example of such a seal is sometimes found within an axle's bearing to help prevent the leakage of the oil lubricating the bearing....

 created by the threads; upon a positive seal between the threads created by the deformation of the threads when they are tightened to the proper torque; and sometimes on the presence of a sealing coating

Coating

Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...

, such as thread seal tape

Thread seal tape

Thread seal tape, or teflon tape can be used in many ways, the most common use in America is to seal things. Thread seal tape — commonly known as "Teflon tape", "PTFE tape", "tape dope", or "plumber's tape"–is a polytetrafluoroethylene film cut to specified widths for use in sealing pipe...

 ("Teflon tape"), or a liquid or paste pipe sealant such as pipe dope

Pipe dope

Pipe dope is slang for thread lubricants, thread sealing compounds and anaerobic chemical sealant that is used to make a pipe thread joint leak proof and pressure tight...

.