Term (literally "concerning the olfactory nerve") for the perception of odour (olfactus = smell) via the receptors in the nose as opposed to the perception of taste via the tongue and palate. The olfactory nerve (lat. Nervus olfactorius) is the first and shortest of the 12 cranial nerves. It is responsible for transmitting olfactory impressions from the olfactory mucosa (2 x 5 cm²) in the upper part of the nasal cavity, which is twice the size of a postage stamp in humans, with 20 million olfactory cells(receptors) to the primary olfactory cortex in the cerebrum. The sense of smell is the most complex chemical sense. It depends on the individual quantity of an olfactory substance from when it is perceived and can be interpreted. This is called the perception threshold (perception limit).
In the context of a wine evaluation (tasting) or wine appeal (description) a distinction is sometimes made between "nasal" (also pronasal or orthonasal) when inhaling via the nose and "retronasal" when exhaling via the nasopharynx. However, two sensory systems are involved in olfactory perception. In addition to the olfactory system, this is also the nasal-trigeminal system with a share of about 30%. Smell and taste interact and influence each other, however, and it is therefore not possible to differentiate exactly. See the other two senses under gustatory (tasting) and trigeminal (tactile = feeling, touching). See also Aroma and flavouring.
Graphics: From Chabacano - from Brain, mouth anatomy,
by Patrick J. Lynch, medical illustrator, CC BY-SA 2.5, Link