What is the Casimir Effect?

TV Squad wrote:

Lost: There's No Place Like Home, Part Two (season finale)

...I tried to read up on the Casimir effect and negatively charged exotic matter, but it's way over my head. I'll stick with learning about philosopher Jeremy Bentham...

Ironically, this week's Economist has an article on potential practical applications of the Casimir effect called "Much ado about nothing"... Coincidence?!