Pipe

A pipe is a man-made channel, closed on all sides, generally round in cross section, for transporting or guiding a fluid substance.

"Pipe" may also be used to refer to certain musical instruments such as the flute, the recorder, the [pan pipe]? and the bagpipe (almost always referred to in the plural form "pipes"). Such instruments are characterized as being [reed instruments]? shaped like a pipe or collection of pipes. "Piping" as a verb means playing one of these instruments.

There is also a geological "pipe" which it is up to someone else to describe.

See: exhaust pipe, smoking pipe, [water pipe]?