Plural of coastline; the outlines or boundaries where land meets the ocean or sea.
Compound of 'coast' and 'line' (from Latin linea). The term became standard in geography and mapmaking during the 18th century as countries precisely documented their borders.
Here's a mind-bending fact: a coastline's total length depends on how carefully you measure it—zoom in closer and count every tiny inlet and rock, and the coastline gets infinitely longer! This is called the 'coastline paradox' in mathematics.
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