The practice of renunciation and withdrawal to embrace the world in the belief that nirvana could be found within the transience (samsara) of ordinary life.
This is one of the cases that can be confused on the emptiness in Mahayana as well but they believed that emptiness is nothing and they can find Nibbhana within this life after realizing of it, not the end of life. Mahayana also used it as to see the ultimate reality and motive their followers to realize that everything can be changed. Of course, when we realize the truth, there is nothing. Even in this life, you can find Nibhana. I don’t think so; it is easy as they thought.