A pipe is a unidirectional data channel for inter-process communication. It's defined by two 📁 File Descriptors, one specifying the reading end and the other for the writing end.
The pipe provides a buffer for processes to write data and another process to read the data. When a process reads from the pipe, it'll wait until an EOF is detected; this occurs either when it reads something that finishes or when all write ends of the pipe are closed.
In the unix shell, a pipe can be easily created between two commands, cmd1 | cmd 2, so that the stdout of the first command is redirected to stdin of the second.