Loka: 'world', denotes the 3 spheres of existence comprising the whole universe, i.e. 1 the sense-world kāma-loka or the world of the 5 senses; 2 the fine-material world rūpa-loka corresponding to the 4 fine-material absorptions see: Jhanas 1-4; 3 the immaterial world arūpa-loka corresponding to the 4 immaterial absorptions see: Jhanas 5-8.
The sense-world comprises the hells niraya the animal kingdom tiracchāna-yoni the ghost-realm peta-loka the demon world asura-nikāya the human world manussa-loka and the 6 lower celestial worlds see: deva I. In the fine-material world see: deva II still exist the abilities of seeing and hearing, which, together with the other sense abilities, are temporarily suspended in the 4 absorptions. In the immaterial world see: deva III there is no materiality whatsoever, only the four mental groups see: khandha exist there.
Though the term loka is not applied in the Suttas to those 3 worlds, but only the term bhava 'existence' e.g. M. 43, there is no doubt that the teaching about the 3 worlds belongs to the earliest, i.e. sutta-period, of the Buddhist scriptures, as many relevant passages show.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.