NAD+ and NADH are two forms of the coenzyme nicotinamide adenine dinucleotide (NAD). These two forms of NAD are a
"redox couple" which means NAD+ can convert to NADH and vice versa. When NAD+ is reduced, it gains a charged hydrogen molecule (H+) and two electrons and converts to NADH, which is oxidized (it looses electons).
The conversion of NAD+ to NADH, and vice
versa, are essential reactions in creating ATP (and therefore cellular energy) during cellular respiration.
