Spelt is a cereal grain in the wheat family, but it is not the same thing as wheat (same genus, different species). The grain has been cultivated for centuries, in both central Europe and the middle east. This is the finely milled meal of spelt, an ancient variety of wheat and sub-species of common wheat. It looks very similar to wheat in appearance, but it has a much harder outer shell before it has been milled. It has a nutty and slightly sweet flavor, similar to that of whole wheat flour. It does contain gluten, so one of the reasons that spelt is rather popular is that it is easy to substitute it into all wheat cookie, bread, etc. recipes, where you will get to enjoy the flavor of spelt without dramatically compromising the texture of your baked good.
Another reason that spelt flour is popular is that it has a fairly strong nutritional profile. Spelt has slightly fewer calories than wheat flour and is somewhat higher in protein. The flour is easy to digest but is lower in fiber than wheat.