This is a Wikipedia article that explains what smoke is. Smoke is a colloid and comprises a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly a by-product of fires.
This is an excerpt from Dave Dodson's video - "The Art of Reading Smoke". This segment allows you to practice some of the skills that are taught in his program.