Charles Piesse, a 19th century perfumer, likened the creation of fragrance to a composer creating a symphony.

Music may be envisaged as having a base note of rhythm, melodic middle notes, and a touch of sparkle from a triangle or piccolo representing the top notes. The harmony of these elements is the 'music'.
The creation of fragrance can be explained using this symphony metaphor in which fragrance 'notes' combine to create the harmonious chord that is the perfume.

A fragrance's volatility dictates how quickly it is perceived and how long it then lingers. The 'higher' the fragrance note, the more volatile it is.
fragrance pyramid

Top notes are small and radiant, and can be perceived immediately by the nose due to their light structure. These are typically citrus, fruit or floral fragrances.

Middle notes are described as the 'heart' of the fragrance. Once the top note of the fragrance has faded, the deeper fruits, spices and floral will reveal themselves.

The Base notes of the fragrance give a perfume its richness. The base note lingers beneath the symphony, and is often a combination vanillas, musks, woods or deep spices. This part of the fragrance is that which creates the lingering impression of the fragrance.