The Nexus is a term for a set of multi-fandom role-playing communities on LiveJournal where anyone can make a journal for a character and participate. The term spans over several communities, including Dear Multiverse, Sages of Chaos, Transgression, and various smaller communities. The first use of the term "nexus" was in the Lunatic Cafe community, which is one of the oldest multi-fandom role-playing communities, and uses the concept that the Cafe is located in an interdimensional nexus permitting characters from different realities to meet.
Some facets of the Nexus exist primarily as advice columns, where characters are expected to ask a question that other characters can answer. Other facets are primarily for role-playing, where posts are written as short stories, as if the players were all contributing to a round-robin style story.
In role-playing terms, it is an intradimensional space where alternate and non-alternate realities meet and occasionally collide. It would not be impossible for one to see Greg Sanders or Zordon conversing with Xander Harris, or Seamus Harper with Bobby Briggs or Hastur. Often, you can get alternates of the same character, which makes it possible to watch spectacles such as Spider-Man, Doctor Octopus, or Mega Man talking to themselves. Depending on who they are, some characters can enter The Nexus as a real place or as a textual-based Internet site similar to any other Livejournal community.
One rule: This site is not accessible In Character. At all.