Smear (optics)
In optics, smear is used to refer to motion that has low temporal frequency relative to the integration/exposure time. This typically results from a relative rate of the image with respect to the detector (e.g., caused by movement in the scene). Smear is typically differentiated from jitter, which has a higher frequency relative to the integration time. Whereas smear refers to a relatively constant rate during the integration/exposure time, jitter refers to a relatively sinusoidal motion during the integration/exposure time. The equation for the optical modulation transfer function associated with smear is the standard sinc function associated with an extended sample

where  is the spatial frequency and  is the amplitude of the smear in pixels. References

Imaging
Science of photography