a class of persons outside the social and spiritual divisions of Vedic culture, whose standards and practices are considered abominable.

A barbarian.

Mleccha (from Vedic Sanskrit म्लेच्छ , meaning "non-Aryan, barbarian") is a derogatory term for people who did not conform with conventional Hindu beliefs and practices.

Literally, "a fondness for defilement." Those who like unclean places and hold evil knowledge and views.