Does the concept of Gentile exist in Christianity? Judaism and Bani Israel have concept of Gentile to represent the pagans and Idolaters with a corpus of rules dealing with them, So does Christianity inherit this concept? If yes where ? and Are Jews considered to Be gentiles by Christians as its known that Jews consider the Christians to be Gentiles and Avodah Zarah?
The term Gentile in the Bible simply means non-Jew or non-Hebrew. In Old Testament times, the Hebrews called the other non-Hebrews as Gentiles and in the New Testament, non-Jews are Gentiles. 

In the New Testament, Paul was famous for preaching to the Gentiles. Because Paul was a Jew, he was zealous for his own people and preached the gospel mostly to the Jews first. But later, as his own people rejected him, his focus shifted towards the Gentiles.


  Romans 10:1 (NIV) Brothers and sisters, my heart’s desire and prayer
  to God for the Israelites is that they may be saved.
  
  Acts 18:5-6 (NIV) When Silas and Timothy came from Macedonia, Paul devoted himself exclusively to preaching, testifying to the Jews that
  Jesus was the Messiah. But when they opposed Paul and became abusive,
  he shook out his clothes in protest and said to them, “Your blood be
  on your own heads! I am innocent of it. From now on I will go to the
  Gentiles.”
  
  Romans 11:11 (NIV) Again I ask: Did they stumble so as to fall beyond recovery? Not at all! Rather, because of their transgression,
  salvation has come to the Gentiles to make Israel envious.


According to New Testament, anyone who is not a Jew is a Gentile, whether he is a Christian or not. And believe it or not, most of the users in this site are Gentile Christians.

Some recent new Christian sects call all non-Christians including Jews as Gentiles but it's not biblical. All non-Jews are Gentiles but non-Jews who are non-Christians are more appropriate to be referred to as Pagans, Heathens, Infidels or simply non-believers, depending on the target.