If you call a woman curvaceous, you are saying her body has full, round curves — waist, hips, chest — and that you find that shape attractive. People use it about women, not about men, and not about things: a bottle can be curved, but nobody calls it curvaceous. The word is American, from the 1930s, and it still sounds a bit like magazine and film-poster talk. It is not a doctor's word. Though actually, it is a looking-at word more than a talking-to word; some women like it, and some feel it treats a body like a picture. Younger speakers often prefer plainer words like curvy, or they avoid body comments altogether.