Refer to http://en.wikipedia.org/wiki/Unix_domain_socket (For personal research)
A Unix domain socket or IPC socket (inter-process communication socket) is a data communications endpoint for exchanging data between processes executing within the same host operating system. While similar in functionality to named pipes, Unix domain sockets may be created as byte streams or as datagram sequences, while pipes are byte streams only. Processes using Unix domain sockets do not need to share a common ancestry. The programmer’s application interface (API) for Unix domain sockets is similar to that of an Internet socket, but does not use an underlying network protocol for communication. The Unix domain socket facility is a standard component of POSIX operating systems.
Unix domain sockets use the file system as address name space. They are referenced by processes as inodes in the file system. This allows two processes to open the same socket in order to communicate. However, communication occurs entirely within the operating system kernel.
In addition to sending data, processes may send file descriptors across a Unix domain socket connection using the sendmsg() and recvmsg() system calls.
Extra: unix domain sockets guide