**Core Concept**
The question is testing the student's knowledge of the most common type of glial tumor, which is a type of brain tumor that arises from the glial cells. Glial cells provide support and structure to the nervous system, and glial tumors can be benign or malignant.

**Why the Correct Answer is Right**
The correct answer is Astrocytoma, which is a type of glioma that arises from astrocytes, a type of glial cell. Astrocytomas are the most common type of glial tumor and can range from low-grade (WHO Grade I) to high-grade (WHO Grade IV) tumors. They can occur in any part of the brain, but are most commonly found in the cerebral hemispheres. Astrocytomas are composed of cells that resemble normal astrocytes, but have abnormal cellular features, such as increased cellularity, nuclear atypia, and mitotic activity.

**Why Each Wrong Option is Incorrect**
**Option A:** Oligodendroglioma - This is a type of glioma that arises from oligodendrocytes, another type of glial cell. While it is a common type of glioma, it is not the most common type of glial tumor.

**Option B:** Ependymoma - This is a type of glioma that arises from ependymal cells, which line the ventricles and central canal of the spinal cord. While it is a type of glial tumor, it is not the most common type.

**Option C:** Meningioma - This is a type of tumor that arises from the meninges, the protective membranes surrounding the brain and spinal cord. While it is a common type of tumor, it is not a type of glial tumor.

**Clinical Pearl / High-Yield Fact**
Astrocytomas can be challenging to diagnose and treat, and their prognosis depends on their grade and location. It is essential for clinicians to be aware of the different subtypes of astrocytomas and their characteristics to provide accurate diagnosis and treatment.

**Correct Answer: C. Astrocytoma**