A suffix added onto a word to denote a scandal involving the base word. The suffix originated from the Watergate Complex in Washington, DC where the scandal leading to the resignation of President Nixon took place. Watergate, strangely enough, was not a scandal involving water.
Examples include Strippergate (one of several scandals involving politicians and strippers), Nipplegate (the wardrobe malfunction at Super Bowl XXXVIII), and Maidgate (Meg Whitman's illegal immigrant maid).
Bill Gates: "Sup dogg."
Steve Jobs: "Not much playa, just tryin' to keep it gangsta."
Bill Gates: "I think I'm going to put up a new gate at my house."
Steve Jobs: "Oooh scandalous!"
Bill Gates: "No, not really, it's just a gate, like a door in a fence."
Steve Jobs: "What kind of -gate? Are you going to hire illegal immigrants to build it? Are you going to paint 'Google is Microsoft's bitch' on it?"
Bill Gates: "No, no, just a regular old gate. Not a -gate as in a scandal."
Steve Jobs: "I can see it now: Gatesgategate! Just make sure you chiggity-check yo self before you wriggity-wreck yo self, sport."
Bill Gates: "Riiight..."