a term generally used to describe a person of Jewish parentage and background who does not necessarily actively practice Judaism, but still identifies with Judaism or other Jews culturally or fraternally, or both. The term ethnic Jew does not specifically exclude practicing Jews, but they are usually simply referred to as "Jews" without the qualifying adjective "ethnic". The term can refer to people of diverse beliefs and backgrounds because genealogy largely defines who is "Jewish". "Ethnic Jew" is sometimes used to distinguish non-practicing from practicing (religious) Jews. Other terms include non-observant Jew, non-religious Jew, non-practicing Jew, and secular Jew. The term may also refer to Jews who do not practice the religion of Judaism. Typically, ethnic Jews are cognizant of their Jewish background and may feel strong cultural (even if not religious) ties to Jewish traditions and to the Jewish people or nation. Like people of any other ethnicity, non-religious ethnic Jews often assimilate into a surrounding non-Jewish culture, but, especially in areas where there is a strong local Jewish culture, they may remain largely part of that culture instead. "Ethnic Jews" include atheists, agnostics, non-denominational deists, Jews with only casual connections to Jewish denominations or converts to other religions, such as Christianity, Buddhism, or Islam. Religious Jews of all denominations sometimes engage in outreach to non-religious Jews. In the case of some Hasidic denominations (e.g. Chabad-Lubavitch), this outreach extends to actively proselytizing more secular Jews. Public opinion The 2013 Pew Research study of American Jews found that 62% thought that being Jewish was mainly a matter of ancestry and culture, while 15% thought that it was mainly a matter of religion. Of those who stated themselves to be Jews by religion, 55% thought that being Jewish was mainly a matter of ancestry and culture, while two-thirds thought that it was not necessary to believe in God to be Jewish. Historical European definitions During the Middle Ages there was no need to ask the question "who is a Jew?", because the difference between the Jewish and the non-Jewish community was clear to both sides. For example, a person born to a Jewish family was Jewish, marriages between Jews and non-Jews were not allowed, and the only way to leave the Jewish identity was through not only leaving the religion, but also cutting all ties to the Jewish community, including family and friends. To Medieval Jews the most essential difference between