X-Alt is short for Extreme Altruist, which is an alternate term for members of the Real Life Superhero movement, originally coined by NightBug and later popularized by Zero. The label is derived from the concept put forth in an article titled "Addicted to Being Good? The Psychopathology of Heroism" by Andrea Kuszewski, which postulates that sociopaths and extreme altruists share many qualities, with the only difference between the two defined as sociopaths are self-focused at the expense of others, while extreme altruists are focused on others at the expense of their own self-interest.
A significant subset of the RLSH movement once endorsed the adoption of the X-Alt label. However, as "Real Life superhero" has become the default for news media to use when covering the movement, usage of X-Alt as an identifier is, for the most part, confined within a portion of the community and not known to the general population.
Kuszewski, Andrea. "Addicted to Being Good? The Psychopathology of Heroism." Institute for Ethics & Emerging Technologies - RETRIEVED 3/12/2017
Heroes in the Night; "Introducing: The X-Alts," blog entry by Tea Krulos, March 9, 2011 - RETRIEVED 3/12/2017