(Sanskrit) The ability of the consciousness - not the intellect - to discriminate between illusion and reality.
"By samyama [conscious effort] over the moments and their succession [self-observation], there comes the higher knowledge that is born from discrimination. [ksana tat kramayoh samyamat viveka-jam jnanam. viveka = discrimination, discernment; ja = born of; jnana = knowledge, gnosis]. From that discriminative knowledge comes awareness of the difference or distinction between two similar objects, which are not normally distinguishable by category, characteristics, or position in space. That higher knowledge is intuitive and transcendent, and is born of discrimination; it includes all objects within its field, all conditions related to those objects, and is beyond any succession. With the attainment of equality between the purest aspect of sattvic buddhi and the pure consciousness of purusha, there comes absolute liberation, and that is the end." —Patanjali, Yoga Sutras 3