Butanoic acid, also called butyric acid, has a formula of CH3CH2CH2-COOH. It is found in dairy products and has a deeply unpleasant smell and bad taste. It is found in human vomit and gives it its distinctive smell. The acid is also created by fermentation in the gut.
Butanoic acid is a colorless liquid that can be dissolved in water, ether or ethanol. It's a fairly strong acid that can attack metals.
Butanoic acid is used to make esters, which is usually done by replacing the hydrogen molecule in COOH with a carbon atom attached to three hydrogen atoms. Ironically, esters often smell sweet and taste pleasant.