How to pin a distinct bone in a rig while animating Here is my scenario: A character sitting on a chair is resting his elbow on a table while moving his hand which is controlled by inverse kinematics.

How can I stick or pin the elbow to the table while I animate the hand and the chest?
It all depends on how your rig is made. Here is one tip.

Add an empty to your scene.
Give it a name like ElbowRest-Empty.
Select your Elbow Bone in Pose Mode. Add a constraint "Track To" 
Select "ElbowRest-Empty" as target.

Now in object mode, where ever you move your empty, your elbow bone will follow.
You may need to lower the influence of IK to keep the elbow bone pinned where ever you want too.