Whether the world that we see here and now is the only one with living beings or whether other such regions also exist elsewhere, has always been a matter of inquisitiveness for man. The Hindu purāṇas have given accounts of such bhuvanas or lokas or worlds, though the number of such worlds vary from one description to another.
Mostly it is three worlds that are mentioned, even in the Vedas: Bhūloka, Antarikṣa or Bhuvarloka and Svarloka or Svargaloka. If human beings inhabit Bhūloka, the munis (sages) live in the Bhuvarloka whereas the devas (gods) live in Svarloka or heaven.
Sometimes names of other lokas such as Pitṛloka (the world of manes), Vāyuloka (the world of windgod) or Saptarṣiloka (the world of the Seven Sages) are also found mentioned in the purāṇas.
Quite often, there is a reference to caturdaśabhuvana or fourteen worlds. They are: Bhūloka, Bhuvarloka, Svarloka, Maharloka, Janaloka, Tapoloka and Satya-loka or Brahmaloka.
The six lokas above the Bhūloka are sometimes collectively called ‘Ūrdhva-lokas,’ since they are above this earth.
The other seven lokas, (making up a total of fourteen), and below the earth, called the ‘Adholokas’ or even as ‘Pātālas’ are: Atala, Vitala, Sutala, Talātala, Mahātala, Rasātala and Pātāla.
The denizens of the Ūrdhvalokas are the beings at various stages of higher spiritual evolution. Sinners of various categories inhabit the lower worlds until their sins are exhausted by suffering.
All, except those in this Satyaloka or the Brahmaloka, have to return to this earth for further evolution up to mokṣa or liberation.
See Vyāsabhāṣya on the Yogasūtras (3.26) of Patañjali, for further details.