2. The rapid involuntary movement of the eyes that occurs when an image of interest falls on the retina at a distance from the fovea (small depression), as normally occurs when reading the printed page.
3. The series of small, jerky movements of the eyes when changing focus from one point to another.
4. The abrupt rapid small movements of both eyes; such as, when the eyes scan a line of print.
The saccades can be divided into two distinct groups: the major saccades which are easily observed with the naked eye and the minor saccades that are virtually unobservable without special instrumentation.
The word saccade is borrowed from French. It is derived from Old French sachier, "to shake". In horse riding, a saccade is the brusque shaking given to the reins of a horse which is used as a signal to the horse by the rider.