(idiomatic) Exactly what is necessary or useful in a given situation; something very beneficial or desirable.

(surveying) An optimal network design within a computer. It involves choosing an optimal reference system and revolving it around a certain real number.

(set theory, order theory, loosely) A set that has a given, elsewhere specified partial order. / (set theory, order theory, formally) The ordered pair comprising a set and its partial order.

plural of higher-order function

(computer science) A function that takes one or more functions as an input, and returns a function as a result.

Alternative spelling of stop loss order

(logic) A formal deductive system extended from propositional logic with the possibility to quantify over individuals of the domain of discourse.

A legally binding directive—issued by a court of law, legislature, or other authority—that requires workers who are engaging in a strike or similar labor action to return to work.

(set theory) A set having a specified total order.

(Catholicism) The religious order of friars established by St Francis of Assisi.