Manas, (Sanskrit, “mind”) in Sanskrit means literature, mind, the coordinating organ of intelligence, thought, understanding, perception, and will. In Vedic times manas meant the individual spirit and the basis of speech (vac).
In the Upanishadic period manas is variously treated: sometimes it is closely associated with speech and breath as a triple entity, sometimes considered as the immediate link between the Self, atman, and the senses, The Katha Upanisad pictures manas as the bridle with reins by which the intellect (buddhi), as the driver of the chariot, guides the horses of the senses.
In the darsanas manas is seen as a special, additional sense organ by which thoughts and sensations have access to the atman. In Samkhya philosophy the principle (tattva) of manas together with the intellect (buddhi) and ego (ahamkara) compose the threefold “inner instrument” (antahkarama).
Here manas is an evolute of buddhi-principle and a special kind of sense organ and organ of action that can bridge the internal and external realms.
In general, manas is of philosophical importance as the organ or ordinary waking consciousness, the proper handling of which may facilitate higher consciousness and liberation.
In Buddhist psychology manas is the rational or intellectual faculty of the mind. Manas has both an active and passive function: in the passive mode it is responsible for reception, ordering, and interpretation of data received through the five senses, its operation being triggered by the input on sense-data.
The process in which manas performs this function is the result of conditioning and habit, which can be modified through the exercise of self-awareness. In its active mode manas is responsible for the production of feelings and wishes. According to the Pali canon, it is considered synonymous with citta and vijana. A.G.H.
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, p. 609