A pipeline is a sequence of functions (or the equivalent thereof), composed so that the output of one is input for the next, in order to create a compound transformation. Famously, a shell pipeline looks like "command | command2 | command3" (but use the tag "pipe" for this). It's also used in computer architecture to define a sequence of serial stages that execute in parallel over elements being fed into a pipe, in order to increase the overall throughput.
In a command line interface or shell, a pipeline uses the pipe operator ("|") to take output from one function or command and input it to another. This is done in a series like "command1 | function1 | command2". For questions related to the pipe operator use the pipe tag.
In computer architecture, a pipeline is a process consisting of a sequence of stages that must be performed in serial order over each element passing the pipe, but may execute in parallel over the elements inside, such that the overall throughput does not depend on the length of the pipe. This is utilized by most CPUs' hardware to process instructions.
A similar technique is also done in software (software-pipelining) in order to optimize the parallelism of a given loop by reordering it to arrange data dependencies in a pipelined manner.
