Esters are organic compounds that are formed by the reaction between an alcohol and an organic acid. They have a distinctive fruity smell and are commonly used in perfumes and flavorings. Esters are characterized by their functional group, which consists of a carbonyl group bonded to an oxygen atom, which in turn is bonded to an alkyl or aryl group. They are different from other compounds listed in the options, such as alcohols, ethers, aldehydes, ketones, carboxylic acids, and amines, due to their unique chemical structure and properties.