Also the TLA for Nicotinamide Adenine Dinucleotide, a very common cellular cofactor involved in redox reactions. Dehydrogenases use it to remove (or add, if running the other way) hydride ions from their substrates. Alcohol dehydrogenase for example oxidises ethanol to ethanal which is then broken down further by ALDH (aldehyde dehydrogenase) to pyruvate. In the process NAD is converted to NADH and can be used elsewhere to reduce other substrates. As the name suggests, it is a dinucleotide, logically formed from AMP and NMP (nicotinamide mononucleotide) by joining the phosphates. This is the basis for rossman fold binding - since each half is bound by a separate copy of the fold.