Second-order

Second-order generally indicates an extended or higher complexity. Specific uses of the term include:

in mathematics and logic

• 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 arithmetic, an axiomatization allowing quantification of sets of numbers
• in perturbation theory, a second-order perturbation may be obtained iteratively

in science and engineering

• second-order fluid, an extension of fluid dynamics
• Second-order reaction, in chemical kinetics, a reaction in which the rate is proportional to the square of a reactant's concentration
• a second-order Fresnel lens has a focal length of approximately 50 cm (19.7 in)

in psychology and philosophy

• Second-order desire, the desire to have a desire for something
• Second-order simulacra, a symbol with no real object to represent
• Second-order conditioning, a form of learning from previous learning
• Second-order stimulus, a visual stimulus distinguished by an aspect other than luminance

in religion

• Second Order, the cloistered nuns who are affiliated with mendicant orders of friars