This is a brief sub-gloss. For a fuller reading of this verse, see Madhusūdana, Śaṅkara, or Rāmānuja above.
The understanding that, wrapped in darkness, takes unlawful action to be lawful and lawful action to be unlawful, and knows all things, every object that can be known, as their opposites, that understanding, Partha, is of tamas.
Contemporary English rendering of the Sanskrit bhāṣya, pending scholar review.