Buddhi
Buddhi is the aspect of mind that is attracted to Brahman (i.e., to "Truth" (sat) or "Reality" (dharma)) and makes wisdom possible.
Etymology
Buddhi is a feminine Sanskrit noun derived from *budh, to be awake, to understand, to know. It has the same root as the more familiar masculine form Buddha and the abstract noun bodhi.
Meaning
Buddhi denotes an aspect of mind that is higher than the rational mind and that is attracted to Brahman (i.e., to "Truth" (sat) or "Reality" (dharma)). Unlike manas, which is a composite of mind and ego deriving from an aggrandized "I-sense" that takes pleasure in pursuing worldly aims and sense pleasures, buddhi is that faculty that makes wisdom possible.
Usage
In Samkhya and yogic philosophy both the mind and the ego are forms in the realm of nature (prakriti) that have emerged into materiality as a function of the three gunas through a misapprehension of purusha (the consciousness-essence of the jivatman). Discriminative in nature (बुद्धि निश्चयात्मिका चित्त-वृत्ति), buddhi is that which is able to discern truth (satya) from falsehood and thereby to make wisdom possible.