Pipe
In plain terms
A mechanism connecting one process's output to another's input.
Going deeper
A pipe channels the output of one program directly into another's input, enabling composition of small tools. It chains commands together.
Under the hood
Anonymous pipes (|) connect commands; named pipes (FIFOs) persist; core to the Unix philosophy.
Examples
ls | grep, shell pipelines, Unix philosophy, inter-process communication.
Think of it like...
Like a conveyor belt feeding one worker's output straight to the next.