We describe fuzzy sets of type-2 and look at the definition of some of the available operations. With the aid of the extension principle we suggest some operations for implementing the concept of con- tainment between fuzzy sets of type-2. We discuss the idea of specificity of a fuzzy set. We suggest a procedure for calculating the specificity of a interval value type-2 fuzzy subset. We show the uniqueness of this procedure. We then extend our method to the case of a general type-2 fuzzy subset.