Citta (Pali and Sanskrit) is one of three overlapping terms used in the nikayas to refer to the mind, the others being manas and viññāṇa. Each is sometimes used in the generic and non-technical sense of "mind" in general, and the three are sometimes used in sequence to refer to one's mental processes as a whole. Their primary uses are, however, distinct.
The Pali-English Dictionary suggests citta is heart / mind, emphasizing it as more the emotive side of mind, as opposed to manas as the intellect in the sense of what grasps mental objects (dhammas). Citta is the object of meditation in the third part of Satipatthana, also called Four Foundations of Mindfulness.
"Citta" primarily represents one's mindset, or state of mind. Citta is the term used to refer to the quality of mental processes as a whole. Citta is neither an entity nor a process; this likely accounts for its not being classified as a skandha, nor mentioned in the paticcasamuppada formula.
The complex causal nexus of volitions (or intentions) which one experiences continuously conditions one's thoughts, speech, and actions. One's state of mind at any given time reflects that complex; thus, the causal origin of actions, speech, and thoughts is sometimes associated with the state of mind (citta), in a manner of speaking. This does not mean that it is that causal nexus; it is better understood as an abstract reflection. One's mind-set can be out of tune with one's desires or aspirations. In that it reflects the volitions, the citta is said to go off with a will of its own if not properly controlled. It may lead a person astray or, if properly controlled, directed, and integrated, ennobling one. One may "make citta turn according to" his wishes most effectively by developing skill in meditative concentration which brings mental calm and clarity. An individual undergoes many different states of mind; M.II.27 asks: "Which citta? for citta is manifold, various, and diverse." Generally speaking, a person will operate with a collection of changing mindsets, and some will occur regularly. While these mindsets determine the personality, they are not in control of themselves, but fluctuate and alternate. There is thus the need for the meditative integration of personality to provide a greater, more wholesome consistency.