What is the difference between blastula and blastocyst?

A blastula, in general, is a spherical mass of cells surrounding a fluid formed after 5–8 days of fertilization.

In mammals, the blastula is specifically called a blastocyst. It is characteristically lined by a layer of trophoblast cells and a bunch of pluripotent cells called the Inner Cell Mass (I.C.M) or embryoblast at one end of the blastocyst. the fluid filled cavity is called the blastocoel. The I.C.M develops to form the fetus while the trophoblast develops to form the placenta.