Here's the breakdown:

* NAD+ (Nicotinamide adenine dinucleotide) is an oxidized form of the molecule.

* NADH (Nicotinamide adenine dinucleotide Hydride) is the reduced form.

During reduction, NAD+ gains two electrons and one proton (H+). This is represented by the addition of a "H" to the molecule's name.

NADH plays a crucial role in cellular metabolism, particularly in the electron transport chain, where it carries high-energy electrons to generate ATP.