Tobacco was an agricultural product on the planet Earth processed from the leaves of plants in the genus Nicotiana of the Nightshades family. To extract nicotine, a highly addictive and poisonous substance, humans smoked toacco on Earth until at least the 21st century.
When Quark, Rom and Nog found themselves in 1940s Earth, virtually all of the Humans they encountered were smokers. Quark had a particularly negative reaction to the tobacco smoke. (DS9: "Little Green Men")