Which term describes a sailor who has completed a crossing of the equator?

The term that describes a sailor who has completed a crossing of the equator is "Shellback." This designation is significant within naval tradition, symbolizing that the sailor has undergone the ancient rite of passage known as the Line Crossing Ceremony. This ceremony often includes various challenges and tasks that honor this milestone and its associated culture within the maritime community.

In contrast, a Polywog refers to a sailor who has not crossed the equator, serving as the opposite category to Shellbacks. The terms Mariner and Seafarer are more general descriptors and do not specifically relate to the accomplishment of crossing the equator or the associated traditions. They encompass anyone who navigates or works on the sea but do not convey the unique status achieved through this specific experience.