A silver bullet is the magical weapon which kills the lycanthrope.
A silver bullet is a technology or solution thought to somehow magically solve all (or a majority) of one's problems. Often used in relationship to whatever the media and industry is currently calling sexy. For instance, cell phones, personal digital video recorders and pocket computers, or Java or XML and all the related baggage.
KPV: Fred Brooks ([L1 ], [L2 ]) wrote a famous essay on this topic entitled "No Silver Bullet: Essence and Accidents of Software Engineering," [L3 ] (Computer, Vol. 20, No. 4 (April 1987) pp. 10-19.) It's also included in the latest edition of The Mythical Man-Month [L4 ].