@ZipLine-- I don't blame you because balconette and demi cup bras are becoming more and more interchangeable these days. Technically, balconette is a sub-group of demi cup. Demi cup is any bra that doesn't have a full cup. The major difference is that balconette bras always have a straight line across the top, whereas the demi can be slightly more curved. The balconette is also more lifting than a regular demi cup bra.
A demi cup bra shouldn't be called a balconette, but a balconette can certainly be called a demi-cup.