I have always thought of these sorts of blends this way.
Working from a base of Virginias (wherever they are grown, blenders then include leaf from the eastern end of the Mediterranean. Then
- If the blend is oriental forward, with little or no latakia, I think of it as an Oriental blend. I think of blends like Skiff, EMP, and Presbyterian in this category.
- If the blend is latakia forward, with other oriental tobaccos in the back seat, as it were, it is an English blend. Squadron Leader and Standard fall into this category.
- If the latakia and other orientals are all more balanced, with neither one in control, it is a Balkan. This term was originally used because of the great success of Balkan Sobranie Original Smoking Mixture, back in the day. Note, however, that SG Balkan Flake has no orientals other than latakia, so it is not a Balkan under this definition.
Please note that this is how I think about these blends, and YMMV. Again, all these terms are marketing terms, and are subject to debate, Personally, these days, I've simplified it even more - either a blend has latakia, or it does not.