What does "cast off" mean?

In maritime terminology, "cast off" refers to the action of releasing or letting go of lines or ropes that secure a vessel to a dock or another craft. When a boat is ready to leave a dock or mooring, the crew must "cast off" the lines that hold it in place to allow it to maneuver away freely. This term is integral to the process of departing from a location as it signifies the transition from being secured to becoming mobile.

The other choices refer to different actions that are not synonymous with "cast off." For instance, securing an object involves tying it down or fastening it in place, which is the opposite of what "casting off" entails. Anchoring a boat is about securing it in a specific location, often using an anchor, to prevent it from drifting, while repairing equipment involves fixing or maintaining tools or machinery, none of which relate to the act of preparing a vessel for departure.