It is the scent of a perfume’s fragrance that lingers on the air emanating usually from a wearer and its penetration or ‘pong factor’. In a sense (all the pun intended) it is a measure of strength.
The origin’s are French surprise! surprise! It literally means wake much like the trail left by a boat in the water. Oooooowah!
A perfume with low sillage may be chosen but you’ve have to be off your head.
Don’t get the spelling wrong otherwise you will be indicating the pong of quite another organic origin. Golly!