This seems to be a term that has strayed from its orginal meaning and is ofton missused.
"Big Beautiful Women" and "BBW" were coined by Carole Shaw in 1979, when she launched BBW Magazine. It is used to describe a woman of greater than normal weight. Not always fat, but anyone above normal weight. These days, this is more the "norm" than the typical "average" bodied girl.
Other terms with similar meaning are:
Full-figured or
Rubenesque -
the latter term referring to the art of Peter Paul Rubens, best known for portraying full-bodied women. These woman may have a large body but may or may not have porportioned curves per say.
Voluptuous and zaftig usually connote ripeness, sensuality, and a body shape involving large breasts and wide hips. These woman may be heavier than average, but still maintain a fit body, just bigger curves.
Voluptuous and zaftig seem to be more percise of many of the "BBW" women I see here. These models have more weight than normal, but are still smoking hot in their own way. Ofton, its as much their attitude and self-confidence as its their actual appearance. These woman are NOT fat. There is just more of them to love :-)