The equator is an imaginary line that divides the Earth into the North Hemisphere and South Hemisphere. Its length is about 40,075 km (24,901.5 miles). The equator runs through numerous countries, including Ecuador, Columbia, Brazil, Gabon, São Tomé and Príncipe, Congo, Zaire, Uganda, Kenya, Somalia, and Indonesia. The equator crosses the territorial waters of the island nations of the Maldives and Kiribati, but does not actually touch the land here.

The equator is, in general, warmer and wetter than most other places in the world. The average temperature on the equator is about 80 to 90 °F (27 - 32 °C). This is very balmy in comparison to the Poles — the South Pole has an average temperature of -40 to -50 °F (-40 to -45 °C). The equator is where the world's tropical climates, including tropical rainforests can be found. The Amazon rainforest, the African rainforest, and the Indonesian rainforest — all equatorial — make up the vast majority of rainforest worldwide (small patches of rainforest can be found in other parts of South America and on the island of Madagascar).

The equator has a constant 12 hours of day and night, in contrast to other parts of the world, where the length of the day varies with the seasons. The temperature is relatively uniform throughout the year, there would be no reasons if it weren't for the rainy season (October to March) during which precipitation increases. On a typical day in the rainy season, the day begins hot and sunny, moisture builds throughout the day, and it begins to rain in the afternoon and evening, with possible thunderstorms.

The equator, being home to the world's rainforests, is also the region in the world with the greatest biodiversity. Scientists estimate that two thirds of the world's species are in the rainforest.

The length of the equator has been measured very accurately by geographers and surveyors. According to a 2000 survey, to within a millimeter of accuracy, it is 40,075,035.535 m. Because the Earth bulges slightly around the middle, the equator is slightly longer than an imaginary circle drawn between the Poles.

The equator is also the ideal place to launch a spacecraft, as a spacecraft launching east can take advantage of the Earth's rotation to reduce fuel costs.