Second-order
# Second-order

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
