A pipe is a form of redirection that is used in Linux and other Unix-like operating systems to send the output of one program to another program for further processing.
Redirection is the transferring of standard output to some other destination, such as another program, a file or a printer, instead of the display monitor (which is its default destination). Standard output, sometimes abbreviated stdout, is the destination of the output from command line (i.e., all-text mode) programs in Unix-like operating systems.
Pipes are used to create what can be visualized as a pipeline of commands, which is a temporary direct connection between two or more simple programs. This connection makes possible the performance of some highly specialized task that none of the constituent programs could perform by themselves. A command is merely an instruction provided by a user telling a computer to do something, such as launch a program. The command line programs that do the further processing are referred to as filters.