"Push" means that the server sends information to the clients. The most common model of this is usually called "Publish/Subscribe" because the clients "subscribe" to the server and the server "publishes" information to all the clients when the information is ready on the server.
"Pull" means that the client requests information from the server. The client requests information at the time that the client needs it and gets the current state of information on the server.
Neither one of these approaches are, in general "better" than the other, however, in certain circumstances, or for certain applications, one approach is a better match than the other.
Write once, run anywhere, because there's nowhere to hide! - /. A.C.