I was reading an old Science Fiction Chronicles the other day and came across the term "space elevator" as in, this would be a good place for one -- but what are they? The author didn't really explain what he meant or what it would look like, what it was for.
It's an elevator that goes from the surface of the earth (has to be some point on the equator) to (a bit beyond) geosynchronous orbit, 22,000 miles up. It's for getting stuff into space much more cheaply than rocket launchers.
See the Wikipedia article for much more information.
The concept was originated by Konstantin Tsiolkovsky in the late 19th century, but didn't appear in SF until 1979, when The Fountains of Paradise by Arthur C Clarke and The Web Between the Worlds by Charles Sheffield both appeared at pretty much the same time.