Chord plucking is when you pluck each note in a chord rather than strumming. You don't normally use your little finger for this as it doesn't reach the strings comfortably within the natural span of your hand.

Another use for chord plucking is when your thumb plays a bass line and your other fingers play the rest of the chord. The thumb generally moves down in contrast to the fingers which pull up across the strings.

Jazz comping often requires you to play a complete walking bass line as well as the chords. Comping is short for accompaniment. In a Jazz band the bass player could play this part for you but to play Jazz guitar on your own you need to be able to play various parts at the same time.