A carboxylate is a salt or ester of a carboxylic acid. Carboxylate salts have the general formula M(RCOO)n, where M is a metal and n is 1,2,...; carboxylate esters have the general formula RCOOR'. R and R' are organic groups; R'≠H.
A carboxylate ion is the conjugate base of a carboxylic acid, RCOO−. It is an ion with negative charge.
Read more about Carboxylate: Resonance Stabilization of The Carboxylate Ion, Examples