In semiotics, salience refers to the relative importance or prominence of a piece of a sign. The relative salience of a particular sign when considered in the context of others helps an individual to quickly rank large amounts of information by importance and thus give attention to that which is the most important. This process stops an individual from becoming mentally overloaded with data.
The salience (also called saliency) of an item - be it an object, a person, a pixel, etc. - is its state or quality of standing out relative to neighboring items. Saliency detection is considered to be a key attentional mechanism that facilitates learning and survival by enabling organisms to focus their limited perceptual and cognitive resources on the most pertinent subset of the available sensory data. Saliency typically arises from contrasts between items and their neighborhood, such as a red dot surrounded by white dots, a flickering message indicator of an answering machine, or a loud noise in an otherwise quiet environment.