A self-contained physical and social environment isolated from the rest of civilisation and maintained in a particular state (almost always by transapients). In effect a living museum, displaying an interesting form of society.
Societeums often display the social conditions associated with a particular historical era, and in many cases the inhabitants are mostly, or completely, unaware of their status as exhibits. Unlike a virtual reality simuulation, however, a societeum is invariable a real-life (rl or ril) location, with a fully detailed reconstruction of the desired society and its infrastructure.
One of the largest Societeums is the world Ribblehead, a world where many curious societies are preserved.