Just because you have specifically asked as to what “Cetasika” means I will give a brief introduction. But I have no interest in giving the sources for it, as to where I took it from. It is because I do not want to see any of my Dhamma friends to go into this level of detail. Life is fleeting. It doesn't last as long as we would like. We have precious little time to practice this Dhamma. We cannot even make sense of the simpler discourses in the Sutta Pitaka, so why would one want to go into such?. The Sutta Pitaka consists chiefly of discourses delivered by the Buddha Himself on various occasions. In it the mental factors are beautifully explained, and one need NOT go any further.
“Cetasika” is found in the Abhidhamma. In my opinion it is there for the “I think therefore I am” type – the so called deep thinkers, who are too smart for their own good. Anyway this is what “Cetasika” means:
There are 52 cetasikas (mental factors), which, arising together in various combination, giving rise to what we call the Mind. Of these fifty-two, Vedana and Sanna are treated as two distinct groups. The remaining fifty are collectively called Sankhara. Unlike the Conventional Teachings of the Suttas, the later day intellectualization of the Dhamma came up with Abhidhamma or Paramattha Desana (An Ultimate Doctrine). This Abhidhamma Pitaka is composed of the following works:-- Dhamma-Sangani (Enumeration of Phenomena); Vibhanga (The Book of the Treatises); Katha Vatthu (Point of Controversy); Puggala Pannatti (Description of Individuals); Dhatu Katha (Discussion with reference to Elements); Yamaka (The Book of Pairs); Patthana (The Book of Relations).
Four ultimate things (Paramattha) are explained in order in the Abhidhamma. They are Citta, (Consciousness), Cetasika (Mental concomitants), Rupa (Matter) and Nibbana. The “being” is microscopically analysed and its component parts are minutely described in it.
A citta is a single act of consciousness - "a state of mind." Each citta consists of many components. Consciousness - the basic experiencing of the object is taken seperately. Together with consciousness every citta contains cetasikas or mental factors.
The cetasikas is said to color the citta and give it its distinctive character. By reference to cetasikas, citta is broken down to: a mind that is lustful, a mind without lust, a mind with or without aversion, a mind with delusion or without delusion, a cramped or scattered mind, a developed or undeveloped mind, a surpassable or unsurpassable mind, a concentrated or unconcentrated mind, the freed or unfreed mind. Mind is not identified with as "I" or "mine," not taken as a self or as something belonging to a self. it may be in a pure state or a defiled state, a lofty state or a low state. Likewise this analytical doctrine, this analysis goes on and on and on minutely describing everything. If that is what you want you can start reading the Abhidhamma. Good luck to you!