If you have a bunch of groups of different things, and you group the groups into a bigger group, what do you call the bigger group?
You can use the word supergroup to refer to a group of subgroups. The super- prefix is the opposite of the sub- prefix.
Wiktionary defines supergroup as:
Any group composed of other groups (in any of several contexts)
You could also use the term "metagroup" - it would mean groups about groups in the same way that "metadata" means data about data.
I'd say collection, if you want to avoid ~group terminology.
Other words could be bundle, cluster, pack, package or any of their synonyms. http://www.thesaurus.com/browse/bundle
A group of similar things or people positioned or occurring closely together. Clusters of creamy-white flowers.
The Oxford Dictionary of English, edited by Angus Stevenson and published in 2010
With this definition you could borrow "supercluster" from astronomy:
A giant cluster of galaxies, a cluster consisting of a number of smaller clusters.
Collins English Dictionary — Complete and Unabridged, 14th edition
Either that or "supergroup" which literally means a group of groups works. "Superset" also works, but is more of a mathematical term.
Coalition, maybe? That may apply more to the political arena, but I have heard it used in relation to activist groups, too.
co·a·li·tion ˌkōəˈliSH(ə)n/ noun an alliance for combined action, especially a temporary alliance of political parties forming a government or of states.
"a coalition of conservatives and disaffected Democrats"
synonyms: alliance, union, partnership, bloc, caucus; federation, league, association, confederation, consortium, syndicate, combine; amalgamation, merger "the ruling four-party coalition"
Source: Oxford Dinctionaries Online.
Although it is used more in corporate settings, I've also seen it being in Biology, Astronomy (comet composition), etc.
a large business that is made of different kinds of companies
a composite mass or mixture; especially : rock composed of rounded fragments varying from small pebbles to large boulders in a cement