Phenolic acids, also known as phenolcarboxylic acids, are types of aromatic acid compound. They are also a subclass of a larger category of metabolites commonly referred to as ``phenolics''. The term phenolics consists of approximately 8000 naturally occurring compounds, all of which have one common structural feature, a phenol (an aromatic ring bearing at least one hydroxyl substituent). The broad category of phenolics can be divided into polyphenols and simple phenols, based merely on the number of phenol subunits present.