Canon's AI Servo

AI Servo is Canon's predictive autofocus (AF) system. The name is derived from the use of Artificial Intelligence used to predict the speed and distance of the moving subject. It greatly increases your chance of getting a sharp image when your target is moving. It is the camera's ability to continuously focus on a moving subject, a feature normally only found on digital SLRs. It is generally used by sports or wildlife photographers to keep a moving subject in focus.

Autofocus Servo is normally engaged by switching focus mode to "AI Servo" in Canon or "Continuous" in Nikon followed by half-pressing the shutter release. The camera will continue to focus based on its own focus rules and your settings while the shutter release is half-pressed or fully depressed (actually taking shots). Predictive autofocusing happens whenever AI Servo is on and there's a readable subject with predictable movement where as Shutter release timing is controlled by the photographer for single shots and the first shot in a burst.