"Kiss your browser goodbye: The radical future of media" - Wired, March 1997, Honorary Mention in Galactic Failed Technological Predictions Hall of Fame =)
"Push", in Internet sense, is a fairly simple thing in theory.
In push systems, the client connects to the server, and the server "pushes" information to the client in constant stream. This is useful for following constantly updating information.
The first push program that gained wide acceptance was PointCast. After that, uh, err...
...yes, I guess that the public interest in push things was killed by the fact that those things were fairly useless and didn't work well with the low modem speeds - and besides, no one actually did "pushing", all solutions were more like "constant pull".
These days, we have RSS feed aggregators that do similar things and more efficiently too, but if you call them "push" systems, the developers will probably come around and punch you on the nose.