Buddhi, from a root meaning to awaken or know, is the intellect that judges and determines. In Sāṃkhya it is the first product of matter, the luminous faculty in which pure consciousness is reflected. In Vedānta it is the inner instrument that decides, and its purification makes discrimination possible. The Gītā speaks of the yoga of the buddhi.
Buddhi
The intellect: the faculty of discernment and decision, highest of the inner instruments.