In Java, Sockets are used for network communication between two machines (client and server) over the internet. They are used to send and receive data between two machines using TCP/IP protocol.

Sockets are the end-points of a two-way communication between two machines, and the communication between them follows a specific protocol. The client machine initiates the communication by creating a socket and connecting it to the server socket. Once a connection is established, both machines can exchange information through the socket.

In order to establish a socket connection, the server must be listening for incoming requests on a specific port number. Clients can then connect to this specific port on the server and start sending and receiving data.

Java has built-in classes for creating and handling sockets. The most commonly used classes are Socket for the client-side and ServerSocket for the server-side. With these classes, a Java programmer can create network applications that communicate with each other in real-time.

Socket programming in Java is commonly used for building distributed systems, networked games, and web applications that require real-time data exchange.