Second-order may refer to:
Mathematics Second order approximation, an approximation that includes quadratic terms Second-order arithmetic, an axiomatization allowing quantification of sets of numbers Second-order differential equation, a differential equation in which the highest derivative is the second Second-order logic, an extension of predicate logic Second-order perturbation, in perturbation theory
Science and technology Second-order cybernetics, the recursive application of cybernetics to itself and the reflexive practice of cybernetics according to this critique. Second-order fluid, an extension of fluid dynamics Second order Fresnel lens, a size of lighthouse lens Second-order reaction, a reaction in which the rate is proportional to the square of a reactant's concentration
Psychology and philosophy Second-order conditioning, a form of learning from previous learning Second-order desire, the desire to have a desire for something Second-order stimulus, a visual stimulus distinguished by an aspect other than luminance
Other uses Second Order (religious), the cloistered nuns who are affiliated with mendicant orders of friars