Socket

It is an general abstraction through which programs send and receive data.  Different types of socket correspond to different underlying protocol suites and different stacks of protocol within the suite. 

The main types of TCPIP socket are stream socket and datagram socket.  A stream socket represents one end of the TCP connection.  It consists of an IP addressm a port number and the end to end protocol (TCP).

A socket is created by a socket call which returns a handle to the socket:

int socket(int domain, int type, int protocol)

"Domain" refers to the communication domain, recall that socket API is a generic interface for a large number of communication domains (e.g. AF_INET for IPV4 and AF_INET6 for IPV6).

HSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)

"Type" determines the semantics of the data transmission with the socket.  For example, if the transmission is reliable or message boundary is preserved etc.  Valid values are SOCK_STREAM or SOCK_DGRAM.

"Protocol" refers to the end to end protocol to be used.  Valid values are IPPROTO_TCP or IPPROTO_UDP.  A value of 0 means to use the default protocol for the "Type".

The close() call close the socket.