A bowman stands aiming at a distant target. He takes out an arrow from the quiver and releases it. While the arrow is floating through the air, the bowman takes another arrow from the bundle of arrows in the quiver and fits it in the bow. He is ready to shoot another arrow.
In Vedanta, the above analogy is used to explain Karma. You are that bowman. The quiver of arrows represents Sanchita Karma, that is, the sum total of the karma of all your past lives. All the good and bad actions from your past lives reside in the quiver as residual effects in your future lives.
Out of this quiver, the arrow that you have shot is that portion of the sanchita karma that is responsible for your present body and destiny. This is called Prarabhdha karma. Thus, the portion of the sanchita karma which influences human life in the present incarnation is called prarabdha.
Each lifetime, a certain portion of the sanchita karma, most suited for the spiritual evolution at the time, is chosen to be worked out, during the course of the lifetime.
Subsequently this Prarabdha Karma creates circumstances which we are destined to experience in our present lifetime, they also place certain limitations via our physical family, body or life circumstances we are born into, collectively known as fate or destiny.