Looking back to the era of film cameras, macro photography (or micro) refers to an image enlargement at a 1: 1 or more ratio in a 35mm film frame.
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The macro lens has something called a flat-field focus. A traditional lens will be curved, so the resulting image will be sharp in the center of the subject and progressively diminish toward the edge. Flat-field lenses have a sharp focus from the focal point to the edge, an advantage over regular lenses.
By the way, I always use manual focus when shooting close-ups because AF is usually too slow and inaccurate if it is lacking in lighting or in a short depth of field condition.