Catu-vokāra-bhava: 'four-group existence', is the existence in the immaterial world arūpa-loka see: loka since only the four mental groups feeling, perception, mental constructions, consciousness, see: khandha are found there, the materiality group being absent.
References[]
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.