NAD⁺ stands for nicotinamide adenine dinucleotide and is found in every single living cell, where it serves as an essential cofactor — a substance whose presence is essential for the activity of molecular machines (enzymes) — involved in fundamental biological processes. Merriam-Webster unabridged. The meaning of NAD is a coenzyme C21H27N7O14P2 of numerous dehydrogenases that occurs in most cells and plays an important role in all phases of intermediary metabolism as an oxidizing agent or when in the reduced form as a reducing agent for various metabolites —called also nicotinamide adenine dinucleotide It's a coenzyme called nicotinamide adenine dinucleotide (NAD+), and it's starting to generate some buzz. What is nicotinamide adenine dinucleotide (NAD+)? NAD+ is a coenzyme, or molecule, found in all living cells, and it plays a vital role in energy metabolism and maintaining proper cell functioning. 57hdUgV.