1. People who do not believe in a particular religion, especially those who do not believe in Islam (from a Muslim perspective) or Christianity (from a Christian perspective)
The crusaders viewed the Muslims as infidels.
Os cruzados consideravam os muçulmanos como infiéis.
2. People who lack religious faith or are not believers in any religion
He was accused of being an infidel for his atheistic views.
Ele foi acusado de ser infiel por suas visões ateístas.