What is the blastocyst? Definition:

The blastocyst (Greek blastos = bud) emerges about the 5th day after fertilization from the morula. At this point, the blastocyst is already in the womb.
For the first time in embryogenesis, differentiation of cell types occurs. From the internal cells (embryoblast) the embryo will develop later. The outer cells (trophoblast) initially perform a protective function, as the egg cell (zona pellucida), gradually dissolves and releases the blastocyst. The trophoblast can now grow on the buccal mucosa, thus initiating implantation.
The blastocyst follows in the embryogenesis on the morula and connects to the gastrula.