Socket server for virtual world is an event-driven server application that handles clients' connections and manages the communication between clients.

When a user starts up and connects to the virtual world, the machine that the user uses is a client. The place where the client machine connects to is the server. The server can be one single powerful computer or a cluster of networked computers interconnected within a high-speed local network. The purpose of the socket server is to manage all client's connections and provide centralized logic and control to clients. It may also respond to provide and store persistent information for the virtual world such as user profiles or world state.

Unlike developing an offline single player game where all logic and data are placed in a SWF file, logic and data are distributed into different places in a virtual world.

Most critical game logic, such as business logic that handles virtual money transaction, is located in the server to enhance the security. The server is also responsible to handle all users' actions and behavior, and provides each user the information they need.

On the other hand, clients are in-charge to display the virtual world according to the client-side data and latest data that updates from server-side. Client-side data includes terrain, map, UI, and basic logic.

For example, imagine that there is a player standing in front of a fountain and you can see him in the virtual world. It is the client that renders the fountain sight according to your current position. And the client gets an updated message from the server that there is another player standing in front of the fountain and renders this player. The clients also gets the appearance of that player from the server in order to render it.