From here: What Is a Coffee Blend? (with pictures)
There's more info there also.The phrase “coffee blend” typically refers to a coffee bean mixture that is made up of different roasts, styles, or tastes of coffee, though it can also sometimes refer to coffee drinks that contain flavoring syrups or other additives designed to change their overall taste profile. When coffee purists talk about blends, they are almost always discussing the actual bean mixture that gives rise to the brew in the first place. Mixtures can be made up of beans of different roasts, different varieties, or different flavor profiles.