In an organism’s immune system, phagocytosis is a major mechanism used to remove pathogens and cell debris.

In cell biology, phagocytosis is the process by which a cell engulfs a solid particle to form an internal compartment known as a phagosome. Phagocytosis is involved in the acquisition of nutrients for some types of cells. The process is homologous to eating at the level of single-celled organisms. In multicellular animals, the process of phagocytosis has been adapted to eliminate debris and pathogens from the body.