• is a self insertion of the author.
• has a romance with one or more canon characters, many times the author's lust object.
• is related to the canon characters.
• has a tragic past, like having her family slaughtered by bandits.
• is very beautiful, and many of the male characters are in awe of the beauty. She also is very powerful (although many times she needs her lust object to rescue her).
• disrupts canon, and makes the canon characters act unlike themselves (out of character).

In the Wheel of Time world, a Mary Sue would be someone who is more powerful than Lanfear, perhaps. She might be another Dreamer, like Egwene. She could be the Far Dareis Mai who can slaughter a wetlander army by herself. Maybe she is the innocent Emond's Field girl who loves one of the three ta'veren.

Females are always known as Mary Sues, while males have different names. People call them Gary Stus, Marty Stus, or Marty Sams.