Aposematism (from apo- away, and sematic sign/meaning), perhaps most commonly known in the context of warning colouration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators. It is one form of "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 or other perceivable characteristics. Aposematic signals are beneficial for both the predator and prey, both of which avoid potential harm.
This tendency to become highly noticeable and distinct from harmless organisms is the antithesis of crypsis, or avoidance of detection. Aposematism has been such a successful adaptation that harmless organisms have repeatedly evolved to mimic aposematic species, a pattern known as Batesian mimicry. Another related pattern is Müllerian mimicry, where aposematic species come to resemble one another.