Source: SB 3.21.32 Purport

 There are different manifestations of the Lord. He is one, but He has become many. He divides Himself into two different expansions, one called kalā and the other vibhinnāṁśa. Ordinary living entities are called vibhinnāṁśa expansions, and the unlimited expansions of viṣṇu-tattva, such as Vāmana, Govinda, Nārāyaṇa, Pradyumna, Vāsudeva and Ananta, are called svāṁśa-kalā. Svāṁśa refers to a direct expansion, and kalā denotes an expansion from the expansion of the original Lord. Baladeva is an expansion of Kṛṣṇa, and from Baladeva the next expansion is Saṅkarṣaṇa; thus Saṅkarṣaṇa is kalā, but Baladeva is svāṁśa. There is no difference, however, among Them.