What does "underrun" mean?

Underrun: To run or pass under; especially (Naut.), to pass along and under, as a cable, for the purpose of taking it in, or of examining it. Note: The cable passes over the bows and stern of the boat used, while the men haul the boat along by pulling upon the cable. Totten. To underrun a tackle (Naut.), to separate its parts and put them in order.