Aposematism, perhaps most commonly known in the context of warning coloration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators.[3] Aposematism is one form of an "advertising" signal (with many others existing, such as the bright colours of flowers which lure pollinators). The warning signal may take the form of conspicuous colours, sounds, odours[4] or other perceivable characteristics. Aposematic signals are beneficial for both the predator and prey, both of which avoid potential harm.
Definition from Wikipedia: http://en.wikipedia.org/wiki/Aposematism