1) Benign and malignant central nervous system neoplasms derived from glial cells (i.e., astrocytes, oligodendrocytes, and ependymocytes). Astrocytes may give rise to astrocytomas (astrocytoma) or glioblastoma multiforme (see glioblastoma). Oligodendrocytes give rise to oligodendrogliomas (oligodendroglioma) and ependymocytes may undergo transformation to become ependymomas (ependymoma), choroid plexus neoplasms, or colloid cysts of the third ventricle.

2) A benign or malignant brain and spinal cord tumor that arises from glial cells (astrocytes, oligodendrocytes, ependymal cells). Tumors that arise from astrocytes are called astrocytic tumors or astrocytomas. Tumors that arise from oligodendrocytes are called oligodendroglial tumors. Tumors that arise from ependymal cells are called ependymomas.