Jackstay

The term is mostly used in a marine context and originated on sailing ships.

Note the use of the term 'stay' implies load bearing working rigging.

In diving it is also a line to guide the movements of a diver between the endpoints.

These include: A diving jackstay is a form of guideline laid between two points to guide the diver during a search or to and from the workplace or to support and guide equipment for transport between two points.

A downline is a diving jackstay from an anchor point at or above the surface to the underwater workplace used to control descent, ascent and the transfer of tools, materials and other equipment between the surface and the workplace.

Personnel transfer from USS Rankin by highline, a form of jackstay, 1960.
A jackstay between two ships of the Indian navy
Form of jackstay (also called a spanwire) by the US Navy used to support a hose for refuelling at sea
Jackstay search pattern using two fixed jackstays to define the search area and a movable jackstay to guide the divers on each leg of the search
Snagline search pattern using jackstays to define the search area and guide the divers who drag a line between them to snag the target