Is there a term do refer to a "set of sets" in math, to distinguish set of regular math objet? In mathematics, a set) is a well-defined collection of distinct objects, considered as an object in its own right. for example A = {2, 1, 3} B = {blue, white, red} C = {3, 5, 6} D = {A, C} all the above are sets, A, B, C are regular sets, and D is a set of set. Is there a term do refer to this type of set(D), to distinguish set of other sets (like A, B, C)? "regular" math objet may not be a precise term, "regular" used here to distinguish a set to from a simple/regular one, such as real numbers that could be an operand of an elementary function.

The term " _family_ " is used for sets of sets. This usage is most common when all the elements of the sets in the family are of the same kind (So in your examples $D = \\{A,C\\} = \\{\\{1,2,3\\},\\{3,5,6\\}\\}$ is a more typical example than say $\\{A,B\\} = \\{\\{1,2,3\\},\\{\mathrm{blue},\mathrm{white},\mathrm{red}\\}\\}$). Wikipedia:

> In set theory and related branches of mathematics, a collection F of subsets of a given set S is called a family of subsets of S, or a family of sets over S. More generally, a collection of any sets whatsoever is called a family of sets.