What is gravitation?
That is very general and hard question even though it doesn't seem like.
Gravitation is a natural phenomenon by which all physical bodies attract each other. Gravity is one of the four fundamental forces of nature, along with electromagnetism, and the nuclear strong force and weak force.
In modern physics, gravitation is most accurately described by the general theory of relativity proposed by Einstein which says that the phenomenon of gravitation is a consequence of the curvature of spacetime.