Client is the system that contain Browser Application and can communicate with server is known as client.
Container is a peace of application that is installed inside the Application Server and the program has to deploy inside the container. container can identify server program, debug it and execute it. Example:Tomcat 5.5.9 is a container. JBoss and Glassfish also are container.
Server: The system where the container is installed and responsible to get the request from client is known as Server