A general term for non-Christians is
non-Christian.
However, depending on the context, other terms might be more appropriate:
* People of other faiths: This is a respectful and inclusive term.
* Non-believers: This term includes atheists, agnostics, and those with no religious affiliation.
* Secular: This term refers to those who are not religious or who do not base their beliefs on religious principles.
* Heathen/Pagan: These terms are sometimes used, but can be offensive or have negative connotations depending on the user and the person being described.
* Specific religions: If you know the specific religion, it's best to use that (e.g., Muslim, Jewish, Hindu, Buddhist).
It's important to be mindful of the context and your audience when choosing a term to avoid causing offense or misunderstanding.