Dina - I think in the freaky modeling world, anything over an 8 is a "plus" size. I was talking with my sister tonight, who does fitting sometimes on fashion shoots in NYC, and she says couture dresses are normally a size 6... a STRICT size 6. And her job is to often bring the dresses IN for super skinny models. Model sizing is nowhere the same as real women sizing. The average US woman is a size 12, and that size 12 is constantly being enlarged to fit increasingly heavy women. So... the numbers are always in flux too, to add to your confusion
In the real world, I think 14 and up is a plus size. Some might say 12 and up. There was a really cool magazine a few years back for plus-size women - "Mode" - and it was titled for size 12 and up. Wish it was still being published! The way they put outfits together was so cool and inspiring!