tasyaiva cante kalpo 'bhud
yam padmam abhicaksate
yad dharer nabhi-sarasa
tasya--of the Brahma-kalpa; eva--certainly; ca--also; ante--at the end of; kalpah--millennium; abhut--came into existence; yam--which; padmam--Padma; abhicaksate--is called; yat--in which; hareh--of the Personality of Godhead; nabhi--in the navel; sarasah--from the reservoir of water; asit--there was; loka--of the universe; saroruham--lotus.
The millennium which followed the first Brahma millennium is known as the Padma-kalpa because in that millennium the universal lotus flower grew out of the navel reservoir of water of the Personality of Godhead, Hari.
The millennium following the Brahma-kalpa is known as the Padma-kalpa because the universal lotus grows in that millennium. The Padma-kalpa is also called the Pitr-kalpa in certain Puranas.