Matter is something which has a specific mass and volume and occupy some space, but the smell that we sense in our body does not occupy any space. It is only a sensation that we experience as our senses it the brain processes that information through very weak electrical impulses and tells us about the nature of smell.
However, smell or odour of a substance that gives us the feeling of smell is classified as matter as they are present in gaseous state and travel through atmoshphere by diffusion.