What is "vanillic acid"

n. (context organic compound English) The aromatic carboxylic acid ''4-hydroxy-3-methoxybenzoic acid'' that is an intermediate in the production of vanillin from ferulic acid

Vanillic acid (4-hydroxy-3-methoxybenzoic acid) is a dihydroxybenzoic acid derivative used as a flavoring agent. It is an oxidized form of vanillin. It is also an intermediate in the production of vanillin from ferulic acid.