Motion Blur
The smearing of a moving subject across the frame during exposure.
Measured in
px
In depth
How much blur appears depends on the subject's speed, its direction relative to the sensor, its distance and the focal length — a car crossing the frame blurs far more than the same car approaching. Blur is not a fault but a decision: it is the only cue in a still photograph that conveys speed directly.
Examples in practice
A cyclist at 1/30 s shows blurred legs against a sharp frame, reading as motion rather than as error.