a person who does not believe in your particular religion, denomination or religious tradition. Similar to infidel , but less judgmental. Of course if a person of faith group "A" regards a person of faith group "B" as an unbeliever, then "B" would probably also regard "A" as an unbeliever.
UNBELIEVER
Meaning of UNBELIEVER in English
English glossary of religious terms. Английский глоссарий религиозных терминов. 2012