Diffusion of religion is best described as the process of

The correct answer is - accepting religions traits from another religion into ones one.

The religious diffusion has happened lots of times in the past, nowadays though, it seems to be much harder for people to participate in religious diffusion even though there's lot of cultural diffusion, which is both, interesting and weird.

Religious diffusion can be easily seen in the three Abrahamic religions. The Judaism is the oldest one, but it has been built on the beliefs and traditions of the Sumerians, which is the first diffusion. Than, the Christianity emerged, which was totally based on the Judaism, and after the Islam came to be, and it was based mostly on the Christianity. Also, an example is the Confucianism, which is a product of religious diffusion between the new beliefs, and the basis taken out of the Buddhism.