An ester is a type of organic compound that is formed through the reaction between an acid and an alcohol. It is characterized by the presence of a carbonyl group (-C=O) bonded to an oxygen atom, which is further bonded to a carbon atom. Esters are commonly used as solvents, fragrances, and flavorings. They have a fruity or sweet smell and are often found in fruits, flowers, and essential oils. In this question, the correct answer is "Ester" because it is the only option that represents a specific type of organic compound.