Description : Macro Gallery :

The definition of macro is capturing an image of a subject the same size or larger than life size on the recording media, whether that be film or digital sensor size. For example if you photograph an insect that is 2 cm (3/4 inch) long, it's image will be 2 cm (3/4 inch)long on the film or digital sensor. The smaller the recording media the smaller the subject must be. Cropping an image does not make a close-up image a macro image.

* Nature : Example for Nature : a Rose bud could be put in the Macro gallery but a Rose Bush or even a full blooming rose belongs in Animals/Plants/Nature -> Flowers/Plants gallery. Macro shots of water drops belong in macro > nature too, because water is an element and part of Nature.

* Human: Example for Human: A picture of one human eye could be put in Macro, but a close up of a face belongs in the People / Portrait gallery under Human Close-ups.

* Objects : Example for Objects : an image of a keyhole in a door could be in macro but a zoom in on a door as part of a building should go in Architecture. A flame can be a macro, but a whole candle belongs in Still Life also close-ups of figurines or dolls are usually not macro and therefore belong in the Still Life gallery.
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you can read more here : AR News - Macro Photography VI