What does A2/AD stand for?

Taken together, anti-access/area denial (A2/AD) is a serious challenge that must be addressed.

The government of the United States reaffirmed its commitment in the 2010 Quadrennial Defense Review to strengthen regional deterrence, and to maintain and enhance its military presence in the Asia-Pacific region and also affirmed its intent to tailor regional defense posture to address such challenges as the proliferation of nuclear technologies and theater ballistic missiles, anti-access/area denial capabilities, and other evolving threats, such as to outer space, to the high seas and to cyberspace.