Gastrulation is a crucial phase in embryonic development that occurs after the blastula stage, during which the single-layered blastoderm reorganizes into a multi-layered structure known as the gastrula. This process establishes the three primary germ layers: ectoderm, mesoderm, and endoderm, which later give rise to all tissues and organs in the organism. Gastrulation is characterized by significant cell movement, including invagination, involution, and migration, laying the foundation for the body's architecture. It is essential for proper development and differentiation of the embryo.