...OED

Oxford English Dictionary

...pipe.

Pipes are exclusively unidirectional. There is a related object in Unix called a socketpair. See ``man 2 pipe'' and ``man 2 socketpair'' for more information.

...currently

This is done by pretending this data was typed into a terminal. Since the rlogin session isn't running on a real terminal at the remote end, the kernel provides a bunch of pseudo terminals, ptys, which act like terminals in that they send data to a program through interrupts and allow terminal editing, like back space and kill line.