A server waits for messages requesting something for a client, and when one is received, it attempts to interpret and act upon the message, and send back an appropriate response to the client. A client is a computer program that can communicate with other clients and/or servers. Clients send requests, and receive responses in return.
It is useful to keep the following four concepts in mind when thinking about and working with client-server architectures:
- Client
 - Server
 - Request
 - Response
 
The world is networked, which involves many different clients communicating with other clients, and also with servers.
Each of the Unity deployment platforms illustrates an example of a client:
- WebGL (running in a web browser)
 - Windows and Mac applications
 - Nintendo Switch
 - Microsoft Xbox
 - Sony Playstation
 - Mobile devices, such as tablets...