I’m around a 12-14, depending on the brand an the fit I want. I’m 5’9, 185 lbs. With all due respect to sugaree, I am definitely not willowy, volumptuous or not. 
I certainly agree that you can’t just ask how big a certain size is without knowing the person’s height. I consider myself “not skinny,” but I wouldn’t go so far as “heavy.” However, unless I want high-waters, I can’t wear size 12 in pants unless it’s a “tall” or a “long”–a size 12 or 14 on a woman of average height would definitely . I’ve got a big frame, with broad shoulders, and I am not skinny by any stretch. I’ve recently lost weight, though, when I was a 16 I was definitely starting to get fat.
Just out of curiosity, are there odd sizes? If not, I wonder why they don’t just divide everything by two. 
Some stores offer odd sizes. Walmart, for example, sizes in odds. So does JC Penney’s teen section (I’m not sure about their adult section). I’m a size 14 in evens or 15 in odds. Why some use one number system and one use another, I’m not sure - 14 and 15 seem to be the same size.
Oprah Winfrey would be a size 6.
No. Wait… 14.
No. 8.
No not 8. I mean 12.
Oops. Maybe a 10.
Yeah, that’s it. A 10.
Wait a minute… make that 16.
Oh hell, what day is this?
I once saw a size 11/12. Hmm.
I also saw a “one size fits most” label. Boy, wouldn’t you feel ODD if you weren’t one of the “most” ?
Junior sizes are odd, misses sizes are even. That’s why you often see the 11/12 type sizing at stores that cater to a young/trendy crowd.
Regarding what size a 12-14 is, several factors have to be taken into account. Women’s clothing sizes are not standard, unlike men’s clothes. Clothes also can be cut vastly differently from style to style. We also wear clothes differently, I wear everything too big, but my sister likes her clothes snug. There’s also a difference between American and UK sizes, UK sizes are smaller.
Finally, all those dead end jobs at the mall have come in useful.