The force that makes two objects pull toward each other because of their mass — why a planet stays with a star, why you stay on the ground. In school you will also hear gravity, which is the everyday word for the same idea, especially the pull of the Earth. Gravitation is the more scientific name, the one that shows up in Newton’s law of gravitation and in careful writing about how masses attract. Though actually, teachers sometimes use the two as if they were exact twins; gravity often means ‘the Earth’s pull on us’, and gravitation the general force between any two masses. You do not need that split to use the word, but it is why a textbook may choose gravitation when it is being precise.