Definition: Phagocytosis is a specific form of endocytosis involving the vesicular internalization of solid particles, such as bacteria. It is therefore distinct from other forms of endocytosis such as pinocytosis, the vesicular internalization of various liquids, and recptor-dependent endocytosis. Phagocytosis (literally, cell-eating) is the process by which cells ingest large objects, such as cells which have undergone apoptosis, bacteria, or viruses. The membrane folds around the object, and the object is sealed off into a large vacuole known as a phagosome.