I know what macro photography is, but what makes a macro (or in Nikon's dictionary: Micro) lens macro? For example, I am looking at this and this Nikon 105mm lens and they seem to have similar spec, one is f/2.8 and the other is f/2.0, but one is labeled Micro.
The micro lens can focus a lot closer than the non micro lens. It can in fact focus so close you can fill the frame with objects that are only the size of your sensor (e.g. 22mm). The non micro lens has a minimum focus distance of three feet (91 cm).
Interesting the non-micro lens features "defocus control" which introduces a variable amount of spherical aberration into the image in order to give softer bokeh.
Macro lenses typically also have a long throw on the focus barrel. In other words, you can turn the focus barrel much longer to get from one end of the focus ring to the other, compared to a non-macro lens of the same focal length. This gives the photographer much more ability to control extremely fine focusing details in the image. It also typically makes autofocusing much slower...but I don't know any macro photographers who don't manually focus their shots.