Maleic a. : Pertaining to, or designating, an acid of the ethylene series, metameric with fumaric acid and obtained by heating malic acid.

Example:
what are the empirical and molecular formula of Maleic acid?

Taxonomy
Maleic acid, fumaric acid, free encyclopedia, bromine, compounds, melting point, Physical properties, Maleates, ethanol, maleic anhydride, molecule, cis isomer, trans isomer, stable, acid chloride, Solubility, methanol, Catalytic Hydrogenation.

Defination from the web:
Maleic acid and fumaric acid can normally not be interconverted because rotation around a carbon carbon double bond is not energetically favourable. ... reacts with thionyl chloride or phosphorus pentachloride to give the maleic acid chloride (it is not possible to isolate the mono ...