avashaha.

 bhootagraamaha sa evaayam bhootvaa bhootvaa praleeyate |

raatryaagamevashaha paartha prabhavatyaharaagame || 19 ||
 
That (same) collection of beings, which was created repeatedly, helplessly dissolves during the night, O Paartha, and is (again) created during the day.
 
bhootagraamaha : community of beings
saha : that
eva : only
ayam : this
bhootvaa : having been created repeatedly
praleeyate : dissolves
raatryaagame : during the night
avashaha : helplessly
paartha : O Paartha
prabhavati : created
aharaagame : during the day
 
Previously, we learned about the process of cosmic creation, where all the living and non-living beings in the universe become manifest at the beginning of the day of Brahma. Now, Shri Krishna elaborates on the dissolution aspect. He says that all those beings go into an unmanifest or “frozen” state during the night of Lord Brahma. The very same beings become manifest or “un-frozen” again, when the day of Lord Brahma begins.
 
As we saw earlier, nothing is ever created or destroyed. The very same set of beings becomes manifest and unmanifest. The total number of “beings” in the universe remains the same. Those who die are “born” into a different form. Forms change but the total amount of universal “stuff” remains the same. It is said that there are 8.4 million species, which are nothing but forms. The movie ends, the reel is rewound, and it begins all over again, on and on, without any end in sight.
 
Now, here is one word in this shloka that deserves further attention. It is “avashaha” which means helplessly. Shri Krishna says that all beings, even if they are plants, animals, minerals or humans are helplessly stuck in this wheel of birth and rebirth, otherwise known as the wheel of samsaara. If they do not actively pursue a spiritual path, whatever that path may be, they will never come out of this cycle.
 

Four forms of pralayas or dissolution are enumerated in the Vedas.

Nitya Pralaya: Every night, when we fall into a deep sleep, our consciousness goes through dissolution daily.

Naimittik Pralaya: At the end of Brahma’s day, all the abodes up to the Mahar Lok dissolute, and all the souls residing there become unmanifest. They remain in a state of suspended animation in the body of Vishnu, waiting for the next cycle of creation. When Brahma creates these lokas again, these souls are reborn based on their past karmas.

Mahā Pralaya: At the end of Brahma’s life, this entire universe goes into dissolution. Again, all the souls of the universe unmanifest and stay in the body of Maha Vishnu. Their gross (sthūl) and subtle (sūkṣhma) body dissolve, but their causal body (kāraṇ sharīr) stays. In the next cycle of creation, these souls are reborn based on their past karmas and past sanskārs, which the soul’s causal body stores and carries with it.

Ātyantik Pralaya: This is the dissolution from the clutches of maya that has been binding the soul since eternity. It takes place when the soul finally attains God and is liberated forever from the cycle of birth and death.