New York Consolidated Laws, Estates, Powers and Trusts Law - EPT § 10-3.4 Classification of powers of appointment as to duty to exercise;  imperative and discretionary

(a) A power of appointment is either imperative or discretionary.

(b) A power of appointment is imperative if the instrument creating it imposes on the donee a duty to exercise it, and it may be imperative even though it is exclusive.

(c) A power of appointment is discretionary if the donee is authorized to exercise or not to exercise it.