What does 'coumarin nucleus' mean?

“Coumarin nucleus” is the term referring to the 1,2- benzopyrone nucleus of the coumarin molecule. The coumarin nucleus is a bicyclic heterocycle that has one benzene, and 2-pyrone rings; the pyrone rings have antioxidant properties. More specifically, the pyrone rings provide an increase in anti-lipid peroxidation activity, an increased inhibitory effect on enzymes, and an increase in primary antioxidant activity.