*pipe line*

. 1. 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. +PJC ]

2. fig. an information channel direct from the source. [ PJC ]

3. 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 ]