Basal ganglia is several nuclei in the diencephalon, near the thalamus. They are responsible for regulation of major muscle groups that make postural adjustments and compensate for inertial forces during movement. Depending on who is writing about them, the basal ganglia include the caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra.
Reference: Introduction to Neurogenic Communication Disorders (Eighth Edition) – Robert H. Brookshire [Book Pg. No. 451]