Real Dictionary

equator
singular noun: The equator is an imaginary line around the middle of the Earth at an equal distance from the North Pole and the South Pole.

equator in American English
an imaginary circle around the earth, equally distant at all points from both the North and South Poles: it divides the earth's surface into the Northern and Southern Hemispheres
noun: the great circle on a sphere or heavenly body whose plane is perpendicular to the axis, equidistant everywhere from the two poles of the sphere or heavenly body

equator in British English
noun: the great circle of the earth with a latitude of 0°, lying equidistant from the poles; dividing the N and S hemispheres