When it comes to macro photography and Nikon, what is the difference between a Micro and a Macro [Nikkor] lens?
Is the answer as simple as to say that Nikon uses Micro in its nomenclature for its macro photography lenses?
Historically, "macro" has been reserved for lenses that can make 1:1 or larger reproductions - microscope territory.
Nikon makes (or made) lenses for microphotography that they call Macro-Nikkors. Their engineers therefore decided to call the common-or-garden lenses that only go down to 1:1 for "Micro-Nikkors". See the discussion on Nikon's site here, and on Bjørn Rørslett's site here.
Nikon doesn't have an equivalent to Canons 65mm MP-E lens, which can go down to 5:1, but if they did, it would probably be a "Macro-Nikkor" as opposed to a "Micro-Nikkor".