agree that in most cases curvy mean anything from a little over weight to a lot over weight.
But i did meet a lady from SA who described herself as "curvy" on there but was in fact quite slim. When i asked her about it, she said she didn't want guys to think she didn't have any tits and thought "curvy" implied she had good sized ones!
She should perhaps have more accurately described herself as slim but busty?
Fat is integral to curvy but ...
Women's body shape is partly due to an increased pelvis size, which is thought to have evolved as a result of humans standing upright and also to allow birth of babies with large human brains.
That aside female 'curves' are mostly defined by deposition of body fat beginning at puberty when oestrogens will produce increased fat deposition on breasts, buttocks and thighs rather than on the waist, giving rise to the 'hour glass' shape. In studies this shape is the much preferred one by majority of males, although ironically less so by women who may prefer a more lean look.
There are a lot of curvy punters around and even a few busty ones too
but in men this is not the natural state based on hormone activity and they are overweight/obese, whereas in women hormones dictate that some body fat in certain areas is normal and so women are naturally 'curvy' without necessarily being overweight.
It is shame that the word curvy in SP's descriptions has become synonymous with being obese, when it may actually be describing the most popular female shape in the eyes of men. Ultimately as Rochelle has said accurate photos will be a far better indicator than a description, body measurements or dress sizes.