The Central Line Running Around the Earth
Puzzle 5 of Things to be Grateful For Hard Pack
Question is: The Central Line Running Around the Earth
and the answer is: EQUATOR
Word Meaning:
EQUATOR — (geography, often “the Equator”) An imaginary great circle around Earth, equidistant from the two poles, and dividing earth's surface into the northern and southern hemispheres.
Definitions from Wiktionary.