Why the desperation anto_men? You could just have looked it up anywhere on the Net. Anyway, a chinaman is a wrist spin ball bowled by a left handed bowler. As for its origin, the word chinaman to describe this style of bowling is apparently traced to former West Indian spin bowler Ellis Achong, a left-arm orthodox spinner and the first Test cricketer of Chinese origin. The story goes that Achong bowled a delivery turning from off to leg and got English batsman Walter Robins stumped as a result. As he walked back, Robins apparently remarked, "Fancy being done in by a bloody Chinaman"!
I can't believe that people don't find the term offensive. Of course, with bowlers like Brad Hogg and Paul Adams using it regularly, the style is still quite popular. Michael Bevan and Simon Katich have also used it. But did you know that the most famous practitioner of the art was none other than Sir Garry Sobers?