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 simulation, however, a societeum is invariably a real-life location, with a fully detailed reconstruction of the desired society and its infrastructure.
One of the largest societeums is the planet Ribblehead, a world where many curious societies are preserved.