The "Beauty Trap" is a reference to one of the thirty-six ancient Chinese military stratagems that were applied to Go by Ma Xiaochun in his book "The Thirty-six Stratagems Applied to Go". The beauty trap falls under the final section of the book: "Stratagems When Losing" and is, by Ma Xiaochun's own admission, one of the more strained references in the book.
The stratagem as applied in military matters is the use of a beautiful woman to wait upon and otherwise distract your foe, weakening his will to fight. In Go, Ma Xiaochun likens this to deliberately sacrificing significant numbers of stones in a losing situation in order to compromise your opponent's judgement and sense of balance. The offer of capturable stones becomes a tempting trap with which lure in your opponent.
By falling into this trap, your opponent becomes complacent in his superiority and makes slack or otherwise suboptimal moves. This allows the player in the weaker position to gain opportunities that may otherwise have been unavailable and, hopefully, turn around the game.