Coumaric acid is a phenolic derivative of cinnamic acid having a hydroxy group as substituent at one of the aromatic positions:
o-Coumaric acid (ortho-coumaric acid) m-Coumaric acid (meta-coumaric acid) p-Coumaric acid (para-coumaric acid)
See also Dihydroxycinnamic acid Ortho, meta, and para substitution