Emergency acquisition flexibilities, as used in this part, means flexibilities provided with respect to any acquisition of supplies or services by or for an executive agency that, as determined by the head of an executive agency, may be used—

(a) In support of a contingency operation as defined in 2.101;

(b) To facilitate the defense against or recovery from cyber, nuclear, biological, chemical, or radiological attack against the United States;

(c) In support of a request from the Secretary of State or the Administrator of the United States Agency for International Development to facilitate the provision of international disaster assistance; or

(d) When the President issues an emergency declaration, or a major disaster declaration.