Is an activity that is forbidden or sacred based on religious beliefs or morals?

If you're looking for a Word that describes that, the Word you're probably looking for is tabu or tapu. Tapu can also be applied to a place or even a person; it marks them as set apart somehow and not to be interacted with. A tapu can be general (everyone is expected to obey it) or personal (the activity or place or person is forbidden for a specific person, though not to anyone else in the culture).