A league is an archaic unit of distance used at sea, historically defined as the distance a person or horse could walk in one hour. In maritime terms, it is generally equivalent to three nautical miles (approximately 3.45 land miles or 5.56 kilometers).

Key points regarding the sailing term "league":
Distance, Not Depth: It is a measure of horizontal distance, often misunderstood in literary contexts (e.g., 20,000 Leagues Under the Sea refers to distance traveled, not depth).

Marine League: A standard maritime league is 3 nautical miles, often historically tied to the distance a cannon shot could be fired from shore to mark territorial limits.

Inconsistency: Historically, the league has varied in length, ranging from 2.4 to 4.6 statute miles depending on the country and era.

Nautical Leagues: A French league is 3 nautical miles, while Spanish leagues have ranged from 3.6 to 4.2 nautical miles.

Modern Usage: It is rarely used in modern navigation but still appears in historical accounts and literature.