Order (CTO) are intermodulation perturbations of third order harmonics. CSO intermodulations are produced by one or two carrier frequencies
subject to second order nonlinearity. With only one carrier frequency, the composite second order corresponds to twice the fundamental frequency. Fortwo carrier frequencies, it is the sum or difference of the carrier frequencies, where one carrier frequency must be greater than the other.
Composite second order plays a role in broadband cable networks and CATV systems, where these intermodulation distortions are noticeable.
These distortions are generated by non-linearity of the cable components.