I've personally only ever done this with my calves, but I believe the term is called pulsing. Pulsing is where you use very short movements. When I performed these it was at the request of my PT who had me doing several calf exercises, and at one point I'd do 10 full reps and then 10 pulses.
I haven't found great information, but there is information at http://www.theirongame.net/take-your-training-to-the-next-level-with-%E2%80%9Cpulse-reps%E2%80%9D.html:
Pulse reps, some people call them “burns”, are a little different than forced reps. Forced reps imply performing additional full range reps of an exercise with the assistance of a spotter or your training partner. During these reps you are truly “dwelling in the house of pain.” You need their help to successfully do the reps. Pulse reps or burns are partial movements done entirely by you, with no spotter assistance except when you need to rack the weight at the conclusion of your set.
Here’s an example on how you can use pulse or burn reps: After doing incline barbell presses for 8 reps, you perform an additional 6 reps by pressing the bar off your chest-up for 2” to 4” only. These reps are done entirely by you and the bar only moves a distance of 2” to 4” from the starting position. After doing these for a couple of sets you will quickly realize that your spotter will need to assist you in racking the weight! Here is my list of exercises that work for pulse or burn reps:
• Bench presses – both barbell and dumbbell
• Incline presses – both barbell and dumbbell
• Military presses – both in front and behind the neck barbell only
• Preacher curls – both barbell and dumbbell
• Close grip and decline barbell presses
• Tricep press downs on a cable machine