"Easter eggs at Easter and Christmas trees at Christmas are items used in the celebration of Christian holidays. As they were borrowed from other religious practices and added to the religion over time, they are examples of "

syncretism

Explanation:

Religious syncretism exhibits blending of two or more religious belief systems into a new system, or the incorporation into a religious tradition of beliefs from unrelated traditions. It is contrasted by the idea of multiple religious belonging and polytheism, respectively.

This can occur for many reasons, and the latter scenario happens quite commonly in areas where multiple religious traditions exist in proximity and function actively in the culture, or when a culture is conquered, and the conquerors bring their religious beliefs with them, but do not succeed in entirely eradicating the old beliefs or, especially, practices.

Religions may have syncretic elements to their beliefs or history, but adherents of so-labeled systems often frown on applying the label, especially adherents who belong to "revealed" religious systems, such as the Abrahamic religions, or any system that exhibits an exclusivist approach. Such adherents sometimes see syncretism as a betrayal of their pure truth. By this reasoning, adding an incompatible belief corrupts the original religion, rendering it no longer true. Indeed, critics of a specific syncretistic trend may sometimes use the word "syncretism" as a disparaging epithet, as a charge implying that those who seek to incorporate a new view, belief, or practice into a religious system actually distort the original faith. The consequence, according to Keith Ferdinando, is a fatal compromise of the dominant religion's integrity.[1] Non-exclusivist systems of belief, on the other hand, may feel quite free to incorporate other traditions into their own.

Syncretism

Explanation:

Easter eggs at Easter and Christmas trees at Christmas are items used in the celebration of Christian holidays which were borrowed and added from other religion are examples of Syncretism.

Syncretism or religious syncretism refers to the coming together of two or more religious belief system into a newly system.

It can also means blending of a religious tradition of belief from a complete different tradition. This can be made possible when Many religion are practiced closely and function actively in the tradition.

Syncretism can also be witnessed when a culture has been defeated and those that defeat the culture bring along their religion beliefs with them but they didn't successfully wipe away all the old beliefs and practices.