Kiriya: or Kriya-citta: 'functional consciousness' or 'kammically inoperative consciousness', is a name for such states of consciousness as are neither kammically advantageous kusala nor disadvantageous akusala nor kamma-results vipāka that is, they function independently of kamma. Thus are also called all those worldly mental states in the Arahat which are accompanied by 2 or 3 noble roots greedlessness, hatelessness, unconfusedness, being in the Arahat kammically neutral and corresponding to the kammically advantageous states of a non-Arahat see: Tab. 1-8 and 73-89, as well as the rootless mirth-producing hasituppāda mind-consciousness-element of the Arahat Tab. 72; further, that mind-element mano-dhātu which performs the function of directing āvajjana to the sense object Tab. 70, and that mind-consciousness-element manoviññāna-dhātu which performs the functions of deciding votthapana and directing to the mental object Tab. 71. The last-named 2 elements, of course, occur in all beings.
Together with kamma-resultant consciousness vipāka it belongs to the group of 'kammically neutral consciousness' avyākata.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.