What is a third in the book Ender's game?

Question:

What is a third in the book Ender's game?

Best Answer - Chosen by Asker: A "third" is a derogatory term used toward the third child born to a family.

In the time of Ender's Game, the population of Earth is so large that most of the world had adopted strict population laws, limiting families to only two children. Violation of these laws had severe consequences, such as losing their home, or jobs. The child also could not attend school on the state's dollar. The only reason that Ender was allowed to be born legally, by special waiver of the IF (International Fleet), was because Peter and Valentine, his siblings, were so promising intellectually for the military program, but had personallity issues that made them unsuitable.