A cofactor is a non-protein chemical compound that is essential for the activity of an enzyme. These molecules can be metal ions, like zinc or magnesium, or organic molecules known as coenzymes, such as NAD+ or coenzyme A. Cofactors help enzymes catalyze biochemical reactions by stabilizing the enzyme-substrate complex or participating directly in the reaction. Cofactors can be classified as either tightly bound or loosely associated with the enzyme. Tightly bound cofactors, called prosthetic groups, remain attached during the enzyme's function, while loosely associated cofactors can detach after the reaction. Understanding cofactors is crucial in biochemistry, as they play a vital role in metabolic processes.