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 [pan pipe]? and the bagpipe. Such instruments are characterized as being [reed instruments]? shaped like a pipe or collection of pipes.

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

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