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. This is very nicely explained in the Brahma-saṁhitā (5.46): dīpārcir eva hi daśāntaram abhyupetya. With one candle one may light a second candle, with the second a third and then a fourth, and in this way one can light up thousands of candles, and no candle is inferior to another in distributing light. Every candle has the full candlepower, but there is still the distinction that one candle is the first, another the second, another the third and another the fourth. Similarly, there is no difference between the immediate expansion of the Lord and His secondary expansion.