Metagalaxy is a term referring to a large-scale galactic system. It may refer to
The whole Observable Universe A galactic group or cluster A group of clusters, such as a supercluster The entire system of galaxies making up the large-scale structure of the universe Multiple virtual worlds clustered together as perceived collectives under a single authority
This term is now little used. Historically, it was first referred to the entire observable Universe as an extension of something larger than a galaxy, i.e. the whole observable Universe.