Despite how frequently it's used, few people know what it means. Sic is latin for 'so' or 'thus.' It is used in brackets or parentheses after an error or uncommon usage of a word to indicate that the error or usage was present in the original context. For example, if you're talking about an advertisement, you may want to refer to the copy on the ad. The new ad for Triple X Energy Drink claims it will, "Boost you're (sic) energy to the xxxtreme (sic)." Using (sic) alerts the reader, "Hey, guy, I see it. I know it's weird/wrong/stupid, but that's the way it was written. Please don't spam me with 'I spotted an error...' emails. Thanks."