In geography, an imaginary line on the earth's surface connecting the North and South Poles; used for longitude and time zones.
Japan Standard Time is based on the meridian at 135 degrees east longitude.
In astronomy, the great circle on the celestial sphere passing through the celestial poles and the zenith of a given location.
The passage of a celestial body across the meridian is called 'culmination'.
本初子午線 is the prime meridian (0° longitude), a specific reference meridian.
From Chinese 子午線 (zǐwǔxiàn), literally 'child-noon line', where 子 (rat, north) and 午 (horse, south) represent the north-south direction in the Chinese zodiac system.