What does "delamination" mean?

Delamination: Formation and separation of laminæ or layers; one of the methods by which the various blastodermic layers of the ovum are differentiated. Note: This process consists of a concentric splitting of the cells of the blastosphere into an outer layer (epiblast) and an inner layer (hypoblast). By the perforation of the resultant two-walled vesicle, a gastrula results similar to that formed by the process of invagination.