sanskrit: मुण्डक, means: a shaven headed (a Sannyaasin); the trunk of a tree with the branches chopped off ; a barber. One interpretation is that this Upanishad is meant for the Sannyaasins or will make one a Sannyaasin. It is associated with the Atharvaveda.
The hairs seen from outside exist on the scalp but they cover up the scalp. Like that, this world variety appears on the "substratum" called Consciousness but covers the Consciousness. Mundakopanishad removes the cover of world variety (ignorance of multiplicity/fragmentation) and exposes the One Consciousness, the Substratum, the Reality.
As such, the word "Upanishad" also means (upa+ni+sad) "the nearness or assimilation of which removes completely the ignorance".