A hypothetical former continent in the Indian ocean supposed to be now represented chiefly by Madagascar.

From the Ra Contact: Also called “Mu”; a land mass where the Lemurian civilization developed; sank about 50,000 years ago due to tectonic plate movement; a part of the population survived and migrated to many places in Russia, North America, and South America.

Reference

10.15, 14.4, 21.24-25, 21.27-28, 24.6