The three marks of existence (Skt. trilakṣaṇa; P. tilakkhaṇa; T. phyag rgya gsum; C. sanxiang) or the three characteristics of conditioned phenomena are, in brief:
In the Pali tradition, these three marks are used to distinguish between Buddhist beliefs and non-Buddhist belielfs. According to the Visuddhimagga, realization of the truth of the these three marks constitutes enlightenment.
https://encyclopediaofbuddhism.org/wiki/Three_marks_of_existence