The process of engulfing and ingestion of particles by the cell or a phagocyte (e.g. macrophage) to form a phagosome (or food vacuole), which in turn fuse with lysosome and become phagolysosome where the engulfed material is eventually digested or degraded and either released extracellularly via exocytosis, or released intracellularly to undergo further processing.
Phagocytosis is the mechanism used by many protists (e.g. amoeba) to acquire nutrients. In humans and other multicellular animals, phagocytosis is an important defense mechanism against infection by microorganisms (e.g. bacteria) and the process of removing cell debris (e.g. dead tissue cells) and other foreign bodies.
Steps of a macrophage ingesting a pathogen: