This is a new form of currency in the game. Your diplomatic actions will earn you these favors which can be used in the World Congress to help you or hinder others.

Diplomatic Favors can be earned through Alliances, City States of which you are the Suzerain, success in Scored Competitions, and more.

There are major and minor ways to gain Diplomatic Favor through a game. Some actions will grant a large payout of Favor all at once, and some will grant it slowly over time. Try trading for other players' Favor to strengthen your position in World Congress or save up Diplomatic Favor throughout the game to pursue Diplomatic Victory Points in the later eras.