Paracosm — a detailed imaginary world

A paracosm is a richly detailed imaginary world.

Paracosms are commonly understood to originate in childhood and to have one or more creators.

The creator of a paracosm forms a complex, deeply felt relationship with this subjective universe, which may include real or fictional characters, rules, and conventions.

A paracosm typically has its own geography, history, and sometimes even language.

It is an experience that often begins in childhood and unfolds over a long period of time — months or even years — as a sophisticated “reality” that can persist into adulthood.

Further reading:

Fictional universe - Wikipedia
A One-of-a-Kind Trove Reveals What 19th-Century American Boyhood Was Really Like
Writing in 1897, Ida Farr Nelson remembered the last decade of family life in rural Goshen, New Hampshire, with happiness. Her sons Elmer, Arthur, and…
A detailed attempt by an unidentified Nelson brother to map out the geography of their imagined world
Worldplay as a cognitive strategy
“Now I see why my teachers here in Castalia emphasize modeling a hypothetical place or system (playing at a world, building a paracosm). Because it: * serves as a cognitive strategy/booster for exploration, learning, and creation/work across an entire lifetime, * cultivates useful factors through which you acquire a network