yeast is a greyish-yellow preparation of the yeast fungus obtained chiefly from fermented beer, used as a fermenting agent, to raise bread dough, and as a food supplement. any unicellular fungus that reproduces vegetatively by budding or fission, including forms such as candida that can cause disease.
what is yeast in simple terms
a single-celled fungus that ferments sugar to produce alcohol and carbon dioxide. a commercial product containing living yeast cells that is used in baking to make dough rise and in the making of alcoholic beverages (as wine) yeast. noun.