What is the term for the difference between the true course and the compass course of a vessel?

The term that defines the difference between the true course and the compass course of a vessel is known as "leeway." This concept is crucial for navigators, as it illustrates how environmental factors, such as wind and currents, can affect a vessel's actual path through water.

In navigation, the true course represents the actual path over the ground, while the compass course indicates the course that the vessel's compass shows. Discrepancies can arise due to magnetic variation, which is influenced by the Earth's magnetic fields and can vary by location. Understanding leeway helps boat operators adapt their navigational strategies to account for these effects, ensuring that they reach their desired destination accurately.

In contrast, other terms like bearing, heading, and drift have different meanings. Bearing refers to the angle or direction to a particular point, heading specifies the direction a vessel is pointed regardless of current effects, and drift describes the movement of a vessel caused by external forces like wind or current rather than indicating a difference between compass and true course. These distinctions highlight the particular role that leeway plays in navigation.