The Earth's equator is an imaginary planetary line that is about 40,075 km (24,901 mi) long in circumference. The equator divides the planet into the Northern Hemisphere and Southern Hemisphere and is located at 0 degrees latitude, the halfway line between the North Pole and South Pole.

The name is derived from medieval Latin word "aequator", in the phrase "circulus aequator diei et noctis", meaning "circle equalizing day and night", from the Latin word "aequare" meaning "make equal".

The equator passes through the land of 11 countries: São Tomé and Príncipe, Gabon, Republic of the Congo, The Democratic Republic of the Congo, Uganda, Kenya, Somalia, Indonesia, Ecuador, Colombia, and Brazil. It doesn't pass through Spain.

More Info: en.wikipedia.org