"Antioxidants" has become a strong marketing word in vitamin/nutrition sales. Perhaps someday someone can explain it to me in a way that I find persuasive. For now, that word triggers my hype-sensor more than it satisfies my understanding.
Ordinary everyday metabolic processes produce a certain number of free radicals--unstable molecules that can interfere with the functions of body cells in important ways. Some interference can be with cell reproduction, replacing healthy cells with daughter cells that have DNA damage from the free radicals. Free radicals can also interfere with cell functions, such as the manufacture of enzymes, etc.
Antioxidants join with free radicals in the body to render them harmless. There is only a limited supply of antioxidants, they are supplied mainly by diet. A number of foods, INCLUDING FRESH COFFEE, have a high level of antioxidant chemicals in them which help prevent degenerative changes caused by the free radicals.
Antioxidants are real, and they are a GOOD thing--help you stay physiologically young and healthy. Not hype. ;-D
(Simplified very basic explanation, hope it helps.)