자오선(meridian)의 약어. 지도나 천문학적 맥락에서 경도선 또는 천극을 통과하는 대원을 나타내는 데 사용된다.
An abbreviation for 'meridian,' often used on maps or in astronomical contexts to denote a line of longitude or a great circle passing through the celestial poles.
예문:
"The map key indicated that 'mer' stood for the prime meridian."
"Navigators frequently use 'mer' in their logs when calculating their longitudinal position."