The three worlds are the upper, lower and intermediate planets of the universe

Expressions researched:
"The three worlds are the upper, lower and intermediate planets of the universe"

Srimad-Bhagavatam

SB Canto 1

The three worlds are the upper, lower and intermediate planets of the universe.

SB 1.7.31, Translation and Purport

All the population of the three worlds was scorched by the combined heat of the weapons. Everyone was reminded of the sāṁvartaka fire which takes place at the time of annihilation.

The three worlds are the upper, lower and intermediate planets of the universe. Although the brahmāstra was released on this earth, the heat produced by the combination of both weapons covered all the universe, and all the populations on all the different planets began to feel the heat excessively and compared it to that of the sāṁvartaka fire. No planet, therefore, is without living beings, as less intelligent materialistic men think.