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 Fresnel lens ( ; ; or ) is a type of composite compact lens developed by the French physicist Augustin-Jean Fresnel (1788–1827) for use in lighthouses. It has been called "the invention that saved a million ships." The design allows the ...

, a size of lighthouse lens *

Second-order reaction In chemistry, the rate law or rate equation for a reaction is an equation that links the initial or forward reaction rate with the concentrations or pressures of the reactants and constant parameters (normally rate coefficients and partial react ...

, 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 {{Disambiguation