Discretion is not deference. That statement may seem obvious to some. To many, however, the two terms are interchangeable. They are not. And the distinction is important, especially now that the Supreme Court has eliminated the deference doctrine associated with Chevron U.S.A., Inc. v. Natural Resources Defense Council. Stated succinctly, deference concerned ambiguous statutory terms or phrases (and implicit grants of authority), while discretion often concerns unambiguously broad statutory terms or phrases (and explicit grants of authority). So even with deference gone, agencies that can point to unambiguously broad terms or phrases in the statutes they administer will retain wide latitude to carry out their missions.
This paper, published in the Harvard Journal on Legislation, explores the important distinction between discretion and deference, as articulated by appellate courts, legal scholars, and the Supreme Court itself.