Accessory cord and webbing are the smaller-diameter ropes and flat straps used to build anchors, friction hitches and slings.
Prusik and hitch cords grip a larger rope to act as a backup or progress-capture device. Sewn slings and tubular webbing are used for anchors and load distribution. High-tenacity cords offer more strength at a smaller diameter.
Match the cord diameter to the host rope for a hitch that holds, and use the rated strength of the cord or sling, not the rope it is attached to.