Tart is a word that seems to be fashionable among older people when referring to a young woman whom they perceive to be
devilishly promiscuous, in a
purposefully destructive sort of way. In my mind the word
harlot seems to match as a slightly more derogatory
synonym, though according to my dictionary, harlot is merely a synonym for a
prostitute, a breed of woman about which we aren't really speaking in this case. This word seems to be used in
contrast with other such words; less severe than most but worse than plain promiscuity or a
penchant for excessive
flirtation.
Update: Master Villain informs me that the term tart is "often used for a girl who spends much of her time 'tarted up', or being very image-conscious.