fifo - first-in first-out special file, named pipe
A FIFO special file (a named pipe) is similar to a pipe, except that it is accessed as part of the file system. It can be opened by multiple processes for reading or writing. When processes are exchanging data via the FIFO, the kernel passes all data internally without writing it to the file system. Thus, the FIFO special file has no contents on the file system, the file system entry merely serves as a reference point so that processes can access the pipe using a name in the file system.