Finding a definitive answer does not seem possible. A religious order priest belongs to a religious community, such as the Franciscans, Dominicans, etc., who live out the charism of their founder and often have a particular type of ministry, e.g., education, health care. They usually live in community and take vows of poverty, chastity and obedience. Diocesan priests, also called secular priests, are ordained for a diocese, a geographical area, and generally serve in parishes, although they also assist in schools, hospitals, prisons, etc. Although they do not take the three vows of poverty, chastity, and obedience, diocesan priests do promise to lead a celibate life, to respect and obey their diocesan bishop, and to live a simple lifestyle.
Religious priests take a vow of chastity and diocesan priests promise celibacy.
Each religious order has a founder who was inspired to respond to a specific situation in the history of the Church. Those orders whose mission or charism addresses ongoing concerns tend to survive, but many religious orders have gone into and out of existence in the Church's long history. New religious orders are even beginning in our day and age as women and men strive to apply and live the Gospel in these circumstances. These three vows are also called the evangelical counsels and describe a radical way to live out the Gospel. In each age, they can provide a strong witness to Gospel values in the face of competing or even contrary values in the prevailing culture.