A knock off or fake of a really expensive, often fashion related, item sold for "one hell of a deal". Derived from the watch, Rolex, being a famous 'knocked off' item. Usually purchased from a street vendor, out of the back of a van or in another questionable transaction. And usually of poor quality.
"Check out the watch I got from this guy on eBay! A Rolex... for $50!"
"Dude... that's a Faux-lex. The '5' is upsidedown."