A pipe is a method of stream-based interprocess communication like fifo's and network sockets. After creating a pipe via the pipe(...) system call, you're given two file descriptors that represent the read and write end of the pipe. It's uni-directional which means that one process always writes to the pipe and the other process always reads from it. In short, it's a one-way buffer that lives in memory (i.e. it's fast). It is reliable since every byte written will be read while the pipe exists. And it is FIFO. Pipes are often used between a parent process and its forked children processes.