A Unix ___domain socket or IPC socket (inter-procedure call socket) is a virtual socket, similar to an internet socket that is used in POSIX operating systems for inter-process communication. The correct standard POSIX term is POSIX Local IPC Sockets.
These connections appear as a byte stream network connection but go from the local computer to itself.
In addition to sending data, processes can send file descriptors across a Unix ___domain socket connection using the sendmsg() and recvmsg() system calls.