pipe line

 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]