A line of pipe with pumping machinery and apparatus for conveying liquids, gases, or finely divided solids, such as petroleum or natural gas, between distant points. [Webster 1913 Suppl.]
fig. an information channel direct from the source. [PJC]
the set of stages and processes from the invention or design of a product to its ultimate use, production, or commercial sale. Used commonly in the phrase
in the pipeline, i. e. still in preparation or under development. [PJC]