"Ficton" is another way to say 'verse — it refers to the characters and settings of a world, usually as it has been defined by a single author. The term was coined by Robert A. Heinlein as "a basic or indivisible unit of imagination". The term is used primarily among Speculative Fiction fans. It is possible for two fictons to merge, usually through repeated crossover.
This page just defines the term. See The 'Verse for examples.