noun. 
                    The condition of an invaginated organ or part.
                  
                
                  
                    noun. 
                    The inward movement of the wall of a tissue or cell, to form a cavity; also, the cavity thus formed.
                  
                
                  
                    noun. 
                    The inward movement of one part of the wall of a blastula, to form a gastrula; the process of gastrulation, in which layers of the ovum are differentiated.