tṛtīya-puruṣa - the third Personality; viṣṇu - Lord Viṣṇu; guṇa-avatāra - the incarnation of the material quality of goodness; dui avatāra-bhitara - within the two incarnations; gaṇanā tāṅhāra - He is designated.

“The third expansion of Viṣṇu is Kṣīrodakaśāyī Viṣṇu, who is the incarnation of the quality of goodness. He is to be counted within both types of incarnations [puruṣa-avatāras and guṇa-avatāras].