Technically speaking, the term “ethnicity” is defined as a group of individuals who identify with each other on the basis of any shared aspect (e.g., language, culture, religion, race). That’s the standard definition in anthropology and other fields. But most people, scientists and laymen alike, at least associate the term “ethnicity” with biology, despite its technical definition not necessitating that. All in all, the term “ethnicity” means a group of individuals who (1) identify with each other because of any shared aspect—that’s the technical definition—and (2) probably share ancestry.

The term “ethnicity” is perfect for the Jews because (1) the Jews have traditionally identified with each other on the basis of shared religion—that’s true no matter how technical you want to be—and (2) the Jews by and large share blood from the Ancient Israelites, with some exceptions, and thus the association with biology/ancestry isn’t far off the mark.

However, Jewish ethnic identity is in transition. The Jews are traditionally an ethnic group whose most fundamental distinguishing criterion is religious: the Torah. But in modernity, ethnoreligion is giving way to ethnonationalism. There are countless Jews who identify strongly with their Jewishness while rejecting Judaism and accepting Zionism. The Enlightenment push for secularization has resulted in a partial replacement of the religious criteria of old with the national criteria of new. Judaism and Zionism cooperate and compete with each other for modern Jewish identity. That’s part of why the question of Jewish identity comes up so often. Jewish identity is a confusing mixture of the old and the new: of the religious and the national.