Cetasika: 'mental things, mental properties', are those mental properties which are bound up with the simultaneously arising consciousness citta = viññāna and conditioned by its presence. Whereas in the Suttas all phenomena of existence are summed up under the aspect of 5 groups: materiality, feeling, perception, mental constructions, consciousness see: khandha the Abhidhamma as a rule treats them under the more philosophical 3 aspects: consciousness, mental properties and materiality citta, cetasika, rūpa Thus, of these 3 aspects, the mental properties cetasika comprise feeling, perception and the 50 mental constructions, altogether 52 mental properties. Of these, 25 are lofty qualities either kammically advantageous or neutral, 14 kammically disadvantageous, while 13 are as such kammically neutral, their kammical quality depending on whether they are associated with advantageous, disadvantageous or neutral consciousness.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.