Olfactory means "relating to smell and olfaction." Olfactory stimuli are caused by chemical molecules that reach our nose through the air. There are millions of olfactory receptors in the nose. These are the tips of olfactory neurons located in the olfactory bulbs. Through the olfactory bulbs, olfactory stimuli are transmitted to the primary olfactory cortex and to the orbitofrontal cortex.
Even though we can't smell as well as dogs for example, we can distinguish about 10,000 different odors.
Author: Bart Aben (translated by Melanie Smekal)