What is the term used for the direction of travel on the compass?

The term used for the direction of travel on the compass is "lubber." This refers to the line on a compass that indicates your heading or the direction in which you are moving. The lubber line allows divers and navigators to align their course accurately with landmarks or waypoints during underwater exploration or surface navigation. It is essentially a reference point that simplifies the interpretation of compass readings, ensuring that the diver knows their intended path while in the water.

The other terms, while related to navigation, do not denote the direction of travel. "Degree" refers to the specific angle measurements used to express directions. "Index" is typically a term that applies to reference points or indicators but not specifically to direction in navigation. "Descent" describes the act of going downwards in the water, but it does not indicate a directional heading on a compass. This makes "lubber" the most appropriate term in the context of compass navigation and travel direction.