SB 3.11.37
ayam tu kathitah kalpo
dvitiyasyapi bharata
varaha iti vikhyato
yatrasic chukaro harih
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O descendant of Bharata, the first millennium in the second half of the life of Brahma is also known as the Varaha millennium because the Personality of Godhead appeared in that millennium as the hog incarnation.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The different millenniums known as the Brahma, Padma and Varaha kalpas appear a little puzzling for the layman. There are some scholars who think these kalpas to be one and the same. According to Srila Visvanatha Cakravarti, the Brahma-kalpa in the beginning of the first half appears to be the Padma-kalpa. We can, however, simply abide by the text and understand that the present millennium is in the second half of the duration of the life of Brahma.