Second-order may refer to:

Mathematics

Second order approximation In science, engineering, and other quantitative disciplines, order of approximation refers to formal or informal expressions for how accurate an approximation is. Usage in science and engineering In formal expressions, the English_numerals#Ordi ...

, an approximation that includes quadratic terms *

Second-order arithmetic In mathematical logic, second-order arithmetic is a collection of axiomatic systems that formalize the natural numbers and their subsets. It is an alternative to axiomatic set theory as a foundation for much, but not all, of mathematics. A precur ...

, an axiomatization allowing quantification of sets of numbers *

Second-order differential equation In mathematics, a differential equation is an equation that relates one or more unknown functions and their derivatives. In applications, the functions generally represent physical quantities, the derivatives represent their rates of change, and ...

, a differential equation in which the highest derivative is the second *

Second-order logic In logic and mathematics, second-order logic is an extension of first-order logic, which itself is an extension of propositional logic. Second-order logic is in turn extended by higher-order logic and type theory. First-order logic quantifies on ...

, an extension of predicate logic * Second-order perturbation, in

perturbation theory In mathematics and applied mathematics, perturbation theory comprises methods for finding an approximate solution to a problem, by starting from the exact solution of a related, simpler problem. A critical feature of the technique is a middl ...

Science and technology

Second-order cybernetics Second-order cybernetics, also known as the cybernetics of cybernetics, is the recursive application of cybernetics to itself and the reflexive practice of cybernetics according to such a critique. It is cybernetics where "the role of the observer ...

, the recursive application of cybernetics to itself and the reflexive practice of cybernetics according to this critique. *

Second-order fluid A second-order fluid is a fluid where the stress tensor is the sum of all tensors that can be formed from the velocity field with up to two derivatives, much as a Newtonian fluid is formed from derivatives up to first order. This model may be obtain ...

, 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 In classical conditioning, second-order conditioning or higher-order conditioning is a form of learning in which a stimulus is first made meaningful or consequential for an organism through an initial step of learning, and then that stimulus is us ...

, a form of learning from previous learning *

Second-order desire Higher-order volitions (or higher-order desire), as opposed to action-determining volitions, are volitions about volitions. Higher-order volitions are potentially more often guided by long-term beliefs and reasoning. A first-order volition is a de ...

, the desire to have a desire for something *

Second-order stimulus A second-order stimulus is a form of visual stimulus used in psychophysics in which objects are delineated from their backgrounds by differences of contrast or texture Texture may refer to: Science and technology * Surface texture, the textu ...

, 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