When reading the Bible, especially the New Testament, you will often come across the word Gentile.
What does it mean?
The Catholic Encyclopedia explains the biblical word in the following way.
A word of Latin origin and usually employed in the plural. In the English versions of both Testaments it collectively designates the nations distinct from the Jewish people.
The primary reason why Gentiles are mentioned in the Bible is that, "as descendants of Abraham, the Jews considered themselves, and were in fact, before the coming of Christ, the chosen people of God. As the non-Jewish nations did not worship the true God and generally indulged in immoral practices, the term Gôyîm "Gentiles" has often times in the Sacred Writings, in the Talmud, etc., a disparaging meaning."
Initially there was much discussion amongst the apostles about whether or not to preach to the Gentiles the Gospel of Jesus Christ.
Thankfully St. Paul became the "Apostle to the Gentiles," and took it upon himself to evangelize all people, both Jew and Gentile, making sure that everyone knew of the saving work of Jesus Christ.