1. Neuroglia consisting of phagocytic cells active in immune reactions of the central nervous system.
2. The third type of glial cell, along with astrocytes and oligodendrocytes (which together form the macroglia).

Microglia vary in appearance depending on developmental stage, functional state, and anatomical location. Subtype terms include ramified, perivascular, ameboid, resting, and activated.

Microglia clearly are capable of phagocytosis and play an important role in a wide spectrum of neuropathologies.

It has also been suggested that they act in several other roles including in secretion (cytokines and neural growth factors), in immunological processing (antigen presentation), and in central nervous system development and remodeling.