When the phrase "5 sigma" appeared on scientists' slides during CERN's July 4 Higgs-search update, the audience watching erupted into applause and cheers. They knew it meant the scientists likely had a discovery on their hands.
If this left you scratching your head, you might want to read symmetry's latest "Explain it in 60 Seconds" article on sigma. But if you have a bit more time to spare, you might want to watch this short video featuring Fermilab physicist Don Lincoln.
In the video, Lincoln explains how figuring out whether a discovery is real or just a matter of luck is similar to judging the fairness of a pair of dice. It all comes down to statistics.
Update: You can watch and rate Lincoln's TED Talk here: http://talentsearch.ted.com/video/Don-Lincoln-The-birth-of-the-un;TEDNew-York