"What is Truth? said jesting Pilate; and would not stay for an answer". The same can be asked of "What is fashion photography?"
In the very least — a person in proximity of garments, recorded.
But maybe it's a feeling, a story, or a recipe of geometries that combine the clothing and their wearer to form a single visual entity. In the life of the image, the clothes and person are one.
Or, perhaps it is a visual and emotional expression of a moment when you become so woven into the fabric that you become lost.
Finally, it could be the form the clothes would take if they could live. What story would they tell? Would they run around and sparkle or stand still and be dark?
We're still trying to figure this one out.
 Of Truth, Francis Bacon