The Differences Between Inertial and Gravitational Masses

The concept of inertial mass is related to the objects inertia which tells you how hard is it to change its momentum. In Newton's world F equals MA and M equals GMM over R squared but in principle they could have been totally different. Einstein unified these things in general relativity and told us that actually inertial gravitational masses have to be the same because according to Einstein there is no acceleration due to gravity.