Metaplasia is a change from one epithelium to another.  In this case the tubules of the breast have changed from their normal epithelium to that of a apocrine sweat gland.  In the following low power photomicrograph I have inserted arrows to show areas of apocrine meaplasia.

The photomicrograph below is at high power. Here you can see the apical portion of the cytoplasm shows the typical "apical snout".  Again I have arrows pointing to the "apical snouts".