Hmmm... I don't think it's quite as clear-cut as that.
I was a bit surprised at the definition that David provided because it began with the words "a positive descriptor..." While I don't mind drinking wines that can be described as fat (I have a friend who love to call big, fruit-forward wines "fat and slutty" just so he can hear himself use that phrase

), I've never considered "fat" to be a particularly positive comment to make. Certainly, it suggests a rich mouth-feel, but fruit that isn't bouyed up by some acidity gets tiresome pretty quickly, IMO, particularly so in a white more than in a red wine. Add to that more limitation on ageability, and I just don't see "fat" as such a positive attribute.
I did a quick search to see whether I could find some other wine-related definitions for the term on-line, and found these:
FAT
Fills the mouth in a positive manner. The wine "feels" and tastes a little obvious and often lacks elegance but is prized by connoisseurs of sweet dessert wines. Not quite desirable in a late harvest Moselle Riesling, but appropriate in a classic Sauternes. Fatness/oiliness is determined by the naturally occurring glycerol - (a.k.a glycerin) - content in the wine.
--Wine Tasting Terminology
by Anthony Hawkins
Fat - Full-bodied, bold, ripe, rich, flavor laden, high alcohol wines low in acidity give a "fat" or fleshy impression on the palate.
--www.yourdictionary.com
Flat, fat, flabby
Critical term for a wine without sufficient acidity, therefore lacking "structure."
--Wine Lovers' Page, Wine Lexicon
FAT: Full-bodied, high alcohol wines low in acidity give a "fat" impression on the palate. Can be a plus with bold, ripe, rich flavors; can also suggest the wine's structure is suspect. Usually used as a negative connotation.
--West Coast Wine Net, Dictionary of Wine Terms
The definition David provided was also on-line, on the Epicurean website.
So it appears that the term is not universally embraced as either a negative or positive term. I'm certainly going to re-think how I use the term in tasting notes. Thank you, Nitro Vino, for posing the question; I've found it quite interesting to investigate this just a little bit.
Now, if you ever see a wine described as "
PHAT", that would mean it's a mighty fine wine, and you should be buying it by the case.
