It is sometimes known as primordial wisdom or self-born, naturally inherent wisdom. Brighter than the sun, according to Buddha, it is always within our hearts. External knowledge must connect with this inner wisdom or such knowledge is useless. Inner wisdom reveals your buddha nature and  that is enlightenment. There is nothing else to be realized. When you discover inner wisdom, this world is nirvana. Until you realize it, it is called samsara.