Messenger line

A messenger line or just messenger is relatively light cordage used to pull a heavier cable across a gap or through a tube or duct. The term is also used for a line used to pull or lower a package along a downline or jackstay.
A heaving line is a rope with a weighted end which can be thrown relatively easily across a gap. If it is attached to a heavier line, warp, or chain and then used to pull the heavier line across the gap it is being used as a messenger line. The name "heaving line" refers to the function of being thrown, and "messenger line" to the function of transferring the object it is fastened to.