Why does Rawls think that justice as fairness is an appropriate title for his theory?

Rawls explains this in the introduction to A Theory of Justice. He writes that "the propriety of the name 'justice as fairness'" is that this phrase "conveys the idea that the principles of justice are agreed to in an initial situation that is fair."
This is crucial to the thought experiment that lies behind his argument in the book. Essentially, Rawls asks the following question: what kind of society would people establish if they were in the state of nature and behind a "veil of ignorance" regarding their social standing in this society?
Rawls argues that in this hypothetical situation, the only rational choice for an individual would be to choose a society that provides for equal rights and opportunities for all people. He even suggests that such a society would feature a government with a robust social safety net because a person could never tell if they might be one of the people that would need such assistance. So by this hypothetical choice under "fair" circumstances, a person would logically choose a society where social and economic inequalities are not tolerated as just.
https://www.csus.edu/indiv/c/chalmersk/econ184sp09/johnrawls.pdf