Contrast-detection Autofocus
A focusing method that drives the lens back and forth, measuring image contrast, and settles at the point of maximum contrast.
In depth
It is extremely accurate because it measures sharpness at the imaging plane itself, but it is inherently a search: the system cannot know which way to move until it has tried. That produces the characteristic small overshoot and return, and it makes tracking a fast subject difficult. It remains the most precise method for static subjects and is often used for the final confirmation in hybrid systems.
Examples in practice
Focusing a macro shot of a stationary flower, contrast detection lands more precisely than phase detection alone.