The term "odor" or "odour" refers to the property of certain substances, in very small concentrations, to stimulate chemical sense receptors, which can be either pleasant or unpleasant. It is often described using terms such as sweet, pungent, acrid, fragrant, warm, dry, or sour, and can be referenced to a specific source, such as sewage or apple. The overall set of qualities are sometimes identified as the "FIDOL (Frequency, Intensity, Duration, Offensiveness, Location) factors"
. Odor classification is a complex field, and scientists have tried to establish comprehensive standards for the description, measurement, and prediction of odors. The perception of odors is influenced by various factors, and the description of odors has been based on a single expert’s opinion, lacking external validation
. In the context of information scent, which is a concept related to how users decide where to go next on the web, information scent is a relative concept, and it guides people to webpages that are likely to contain the content they're seeking
. Odor is a property of a mixture of different volatile chemical species capable of stimulating the olfactory system
