(1) A one-way communication path between a sending process and a receiving process.
(2) An interprocess communication mechanism that connects an output file descriptor to an input file descriptor. Usually the standard output of one process is connected to the standard input of another, forming a pipeline.
(3) To direct the data so that the output from one process becomes the input to another process. The standard output of one command can be connected to the standard input of another with the pipe operator. Two commands connected in this way constitute a pipeline.