The ethereal space between he Martyaloka (the earthly abode)and the Svargaloka (heavenly abode), as conceptualised in Purāṇa(s) (Purana; Mythological Scripture) is called Antarīkṣa (Antariksha). Antarā means ‘in between’, and the dhātu (dhatu; verb-root) ‘Īkṣ’ means ‘too see’. The sky, comprising of clouds and the atmosphere — that is seen as lying between the earth and heaven, is called Antarīkṣa. In the ancient Brāhmaṇa (Brahmana) text, Śatapatha Brāhmaṇa (Satapatha Brahmana), Antarīkṣa is defined as follows —
purāntarā vā idamīkṣamabhūditi tasmādantarikṣam.
According to some rules in Vyākaraṇa (Vyakarana; Grammar), the ‘Ī’ of ‘Īkṣ’ dhātu is read as a hrasvasvara, (small vowel), so the spelling ‘Antarīkṣa’ is also valid.

However, since the time of Ṛgveda, there had been a clear understanding that Ākāśa (Akasa; Ether)) and Antarīkṣa are not synonymous terms. At least seventeen ṛṣi(s) (rishi; seer-sage) have described some distinctions between Ākāśa and Antarīkṣa, in the mantra(s) uttered by them. From the mantra uttered by Sage Aucathya Dīrghatamā (Auchathya Dirghatama), it is clear that Antarīkṣa is only a portion of Ākāśa. The expansion of Ākāśa is much greater, even infinite.While composing commentary on the mantra of Aucathya Dīrghatamā, Sāyanācārya (Sayanacharya)has mentioned that the place between heaven and earth, where Kṣiti (Kshiti; Sol), Ap (Water), Teja (Fire or Energy), Marut (Wind)and Vyoma or Ākāśa merge together, and lead to a possibility of the creation of life — that place is called Antarīkṣa —
dyāvāpṛthivyorantarmadhye yoniḥ
sarvabhūtanirmāṇāśrayamantarikṣaṃ vartataḥ iti śeṣaḥ.
In several other mantras in Ṛgveda, uttered by several other sages, the same concept is supported.