From what I understand, NADH does not contain any sodium, so why is it being referred to as a sodium salt? Were sodium ions added to NADH? If so, why were they added? On a related note, why is its oxidized correspondent NAD+ referred to as "free acid"?
The two phosphate groups each carry a negative charge at physiological pH.
NADH (sodium salt) means that at least one of the two negative charges are counterbalanced by Na+. If both are counterbalanced with Na+, it would be better to say "disodium salt".