(2) imaginary line passing round the Earth midway between North & South poles Explanation: An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass. Notably, the Equator refers to the Earth's equator, per above: an imaginary line on the Earth's surface equidistant from the North Pole and South Pole, dividing the Earth into the Northern Hemisphere and Southern Hemisphere. Other planets and spherical astronomical bodies have equators similarly defined. The length of the Equator is roughly 40,075 kilometres.