Named pipe
In computing, a named pipe (also FIFO for its behaviour) is an extension to the traditional pipe concept on Unix and Unix-like systems, and is one of the methods of interprocess communication. The concept is also found in Microsoft Windows, although the semantics differ substantially. Also, NT Named Pipes can inherit a security context. A traditional pipe is "unnamed" because it exists anonymously and persists only for as long as the process is running. A named pipe is system-persistent and exists beyond the life of the process and must be "unlinked" or deleted once it is no longer being used. Processes generally attach to the named pipe (usually a file) to do IPC.
Named pipes in Unix
Instead of a conventional, unnamed, shell pipeline, a named pipeline is explicitly created using mknod or mkfifo, and two separate processes can access the pipeline by name.
For example, one can create a pipe, set up gzip to compress things piped to it
mkfifo pipe gzip -9 -c < pipe > out
in a separate process, independently, one could perform
cat file > pipe
which would then perform the compression by gzip.
Named pipes in Windows
In Windows, the design of named pipes is biased towards client-server communication, and they work much like sockets: other than the usual read and write operations, Windows named pipes also support an explicit "passive" mode for server applications (compare: Unix domain sockets).
Named pipes aren't permanent and can't be created as special files on any writable filesystem, unlike in Unix, but are volatile names (freed after the last reference to them is closed) allocated in the root directory of the named pipe filesystem (NPFS), mounted under the special path \\.\pipe\ (that is, a pipe named "foo" would have a full path name of \\.\pipe\foo). Anonymous pipes used in pipelining actually are named pipes with a random name.
They are very rarely seen by users, but there are notable exceptions. The VMware PC emulator, for instance, can expose emulated serial ports to the host system as named pipes, and the kd kernel mode debugger from Microsoft supports named pipes as a transport for debugging sessions (in fact, VMware and kd can be coupled together - since kd normally requires a serial connection to the target computer - letting driver developers do their development and testing on a single computer). Both programs require the user to enter names in the \\.\pipe\name form.
Named pipes in Windows networking
Named Pipes is also a networking protocol in the SMB suite, based on the use of a special Inter-process communication (IPC) share. SMB's IPC can seamlessly and transparently pass the authentication context of the user across to Named Pipes. Windows NT's entire NT Domain protocol suite of services are implemented as DCE/RPC services over Named Pipes, as are the Exchange 5.5 Administrative applications.
Windows NT Named Pipe authentication inheritance is sufficiently opaque and seamless to the user and developer perspective as to be nearly invisible, and consequently it is frequently misunderstood.