Vipāka: 'kamma-result' or 'effect of action', is any kammically morally neutral mental phenomenon e.g. bodily pleasant or painful feeling, sense-consciousness, etc., which is the result of advantageous or disadvantageous intentional action kamma through body, speech or mind, done either in this or some previous life. Totally wrong is the belief that, according to Buddhism, everything is the result of previous action. Never, for example, is any kammically advantageous or disadvantageous intentional action the result of former action, being in reality itself kamma. On this subject see: titthāyatana kamma, Tab. I; Fund II. Cf. A. III, 101; Kath. 162 Guide, p. 80.
Kamma-produced kammaja or kamma-samutthāna material things are never called kamma-vipāka as this term may be applied only to mental phenomena.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.