In client/server applications, "push" is to send data to a client without the client requesting it. The World Wide Web is based on a "pull" technology where the client browser must request a Web page before it is sent.
Broadcast media are traditionally "push technologies" because they send information out regardless of whether anyone is tuned in. Increasingly, companies are using the Internet to deliver information push-style. In PR (public relations), "push PR" refers to basic PR which is
essentially an outreach effort. It involves creating a story for the
client to market and then packaging it as a press release (or a pitch
or a call).
Online examples of push technologies are e-mail, a portal (on a handhelddevice that supports a microbrowser), paging networks (again Blackberry because it serves more than one function), file transfer, and RSS. The most widely used push technology is e-mail, it is a push technology because you receive mail whether you ask for it or not, that is, the sender pushes the message to the receiver.
In programming, "push" is to place a data item onto a stack. In this case, the opposite of push is "pop" which means to remove an object from a stack.