Phenolic acids constitute a major class of plant-derived secondary metabolites featuring one or more hydroxyl groups attached to an aromatic ring along with a carboxylic acid moiety. Common subclasses include hydroxybenzoic acids (e.g., gallic, protocatechuic) and hydroxycinnamic acids (e.g., caffeic, ferulic, p-coumaric). They function as potent antioxidants by scavenging free radicals, chelating metals, and inhibiting lipid peroxidation. Abundant in fruits, vegetables, grains, and spices, they contribute to color, flavor, and shelf-life stability while offering potential anti-inflammatory, antimicrobial, and cardioprotective effects in human diets. Their bioavailability varies with esterification and matrix interactions.