A socket is a communications endpoint with a name and address in a network. Sockets were made famous by their implementation in Berkeley UNIX, and made universal by their incorporation into Windows.

Most socket-based applications employ a client-server approach to communications. Rather than trying to start two network applications simultaneously, one application tries to make itself always available (the server or the provider) while another requests services as needed (the client or the consumer).

VMware vSockets are designed to use the client-server approach but, unlike TCP sockets, they do not support multiple endpoints simultaneously initiating connections with one another.

Data going over a socket can be in any format, and travel in either direction.

Many people are confused by AF_INET as opposed to PF_INET. Linux defines them as identical. This manual uses AF only. AF means address family, while PF means protocol family. As designed, a single protocol family could support multiple address families. However as implemented, no protocol family ever supported more than one address family. For Internet Protocol version 6 (IPv6), AF_INET6 is synonymous with PF_INET6.

WinSock includes virtually all of the Berkeley sockets API, as well as additional WSA functions to cope with cooperative multitasking and the event-driven programming model of Windows.

Programmers use stream sockets for their high reliability, and datagram sockets for speed and low overhead.