An ester is an organic compound with the formula RCOOR' derived from a carboxylic acid by substitution of the hydrogen atom of the hydroxyl group OH by an alkyl group R'.
Esters are obtained by esterification, which is the action of an acid (which can be a carboxylic acid RCOOH) on an alcohol R'OH with the formation of water in the reaction acid + alcohol -> ester + water.
The reciprocal reaction is hydrolysis.
Esters are compounds of fruit aromas. Animal and vegetable waxes, animal oils and fats are often esters. Many polymers (polyester fibres, polyvinyl acetate) are also esters. Lactones, some of which are used in the perfume industry for their musk smell, are cyclic esters.