The Earth’s circumference is the distance circling around the Earth. Note that the Earth is not a perfect sphere, but rather an oblate spheroid, and so the distance around the equator is slightly larger than the distance from pole to pole.
Equatorial circumference: about 40,075 km
Meridional (pole-to-pole) circumference: about 40,008 km
The Earth’s circumference is often estimated as approximately 40,000 km, and so this is the value you should choose when answering geography and general knowledge questions.