Switchday is the day every year when the Lottery is drawn to determine whose Absolute Locus a citizen will receive for the remaining duration of the year. It began in the year 2013 at the suggestion of /u/SkyWorthy in what has come to be known as the First Switch [1].

"Every person switches location with one random person on the planet. You might switch locations with Bill Gates and end up in his house. Or you might end up in a Somalian jail cell." - SkyWorthy

The mechanisms on which the Lottery runs are not thoroughly understood, and it is believed by many that it could possibly be connected to the individual's Expiration Date [2] or Hovering Number [3].

The Absolute Locus can be at any place or time in spacetime, within the allotted universe(s) and planet(s). The species, age, sex, and other personal qualities of the individual may or may not transfer with the Switch, depending on the rules of their specific planet and/or universe.

In some omniverses, such as The Egg [4], Switchday occurs not annually, but at the mortal biological death of the individual.

[1] /u/SkyWorthy, 2013
[2] /u/shk926, 2013
[3] /u/StoryTellerBob, 2013
[4] The Egg; Andy Weir, 2010