Hebrew, for “the descent (decline) of the generations.” God perfectly taught Moses on Mt. Sinai. But as each generation of men who participated in our fallen nature taught it to their children, tiny errors accumulated over time. Early sages who lived closer in time to Moses, are considered less exposed to yeridat hadorot and therefore more reliable than later ones.
The same is true in the Catholic tradition. The Church Fathers who lived closer in time to Rabbi Yeshua’s shlikhim are considered more reliable than later Fathers. The time interval between the original apostolic teaching and a particular Father is, of course, only one of many factors in that Father‘s reliability. The dominant factor is God’s grace. Some later Church Fathers, such as St. Augustine, are extremely reliable.