Partials are any shortened range of motion lift. Whereas in a deadlift you’ll lift the weight off of the floor, a partial deadlift may have you lift the weight from above or below the knees. Or there is what’s been called the hand and thigh lift or health lift, a very short range movement at the top to lockout.
Partials can be done with virtually any exercise though the most common are done with basic full range exercises like deadlifts, squats, presses and the bench press.
Why would you want to do partials in your training? They allow you to lift heavier weights. This has several benefits. It overloads you body to a point where your previous max (in the full range lift) may feel light. For various sports and athletic activities most movements are partial movements. Think about a punch. Although the hips are heavily involved you don’t drop into a full squat before throwing the punch.
Partials can be mixed in with full range lifts, worked on different days or done with Progressive Distance Training.
Partials also tend to be quite safe despite the large load. Of course, you’ll want to work into them slowly.
For much more on partials check out the Partials Training DVD by Bud Jeffries.