The Queen’s Indian Defense is an extremely solid hypermodern defense against the d4 opening from white. It usually arises if white chooses to avoid the Nimzo-Indian defense by bringing his knight to c3 and instead opts to first bring his knight to f3.
Black now has the option to play b6, preparing to fiachetto his light square bishop and try to take control over both the center light squares as well as the long diagonal.
White has a few options but usually will opt for g3, challenging the long diagonal by fianchettoing his own bishop to g2.
Unlike some of the other Indian defenses, black has many opportunities to play aggressive which makes it very popular at top level play.
Click the video below to watch a detailed explanation of this opening.