Question

What is a supercluster?

Answer 1

Galaxy Superclusters usually consist of chains of around a dozen galaxy clusters, each with a mass of about `10^13 to 10^14` solar masses.

Explanation:

Galaxy Superclusters usually consist of chains of around a dozen galaxy clusters, each with a mass of about `10^13 to 10^14` solar masses. The largest superclusters can be spread over several million light years of space. Ninety percent of galaxies are thought to be located in them!

https://imagine.gsfc.nasa.gov/features/cosmic/nearest_superclusters_info.html

A really good reference with good maps of the nearest superclusters and voids are the Atlas of the Universe pages: The Nearest Superclusters and The Neighboring Superclusters.
http://www.atlasoftheuniverse.com/

Graphics, animation and discussions:
https://www.space.com/27016-galaxy-supercluster-laniakea-milky-way-home.html