Dual Pixel Autofocus
An on-sensor phase-detection design in which every photosite is split into two independently readable halves.
In depth
Because each half sees the scene through a different side of the lens, comparing the two gives a phase difference at effectively every pixel — full-frame coverage with no dedicated AF points and no loss of imaging pixels, since the halves are summed for the final image. The paired readout also encodes a small amount of depth information usable for after-the-fact adjustments.
Examples in practice
Dual pixel coverage lets focus lock onto a face at the extreme edge of the frame, where older systems had no AF points at all.