Other forms: unbelievers
An unbeliever is a person who is skeptical of a particular religion. Most places of worship welcome all people, even unbelievers.
If you're not a believer — that is, if you don't believe in something — you're an unbeliever. This noun usually turns up in religious contexts, either as another word for an atheist (someone who doesn't believe in any god or deity), or simply to denote someone who isn't a follower of a certain religion. If you're a Unitarian, your devout Catholic relatives might consider you to be an unbeliever.