A fixed phagocyte, also known as a histiocyte, is a type of immune cell that resides in tissues and is responsible for engulfing and destroying foreign particles, such as bacteria, viruses, and damaged cells. There are several synonyms for fixed phagocyte, including macrophage, dendritic cell, mononuclear phagocyte, and reticuloendothelial cell. These cells vary in shape and function, but all play a crucial role in the immune system's response to infection and injury. Macrophages are the most well-known subtype of fixed phagocytes and are found in virtually all tissues. Dendritic cells are specialized in presenting antigens to other immune cells, while mononuclear phagocytes and reticuloendothelial cells have more generalized phagocytic functions.