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human
ELI5: if being Jewish is a race or a religion?

I work with some Jewish people (not very well, don't know them enough to ask), both who have converted to Judaism, leading me to believe it is in fact a religion that one can opt in and out of.

But I go to school with a girl who was "born" Jewish but is not practicing. She said that in the community she is still considered Jewish, and that it is not something you can choose not be if you are born into it.

Is it a race, religion, or both? (I hope this isn't an insensitive question)
gpt
Both. Kind of.  
Firstly, it's worth pointing out that what we consider races are really one of about five groups: black, white, Asian, southeast Asian, or Amerindian. <EDIT:> **Most** <END EDIT> Jewish folks are an *ethnic* group that most would consider white.  EDIT 2: There are significant numbers of Jewish populations in India and Asia, and they are...well, primarily Indian and Asian populations.  There are also Jewish populations in Eastern Africa made up of Africans.  But the primary population of people that we would identify as "Jewish" are those who arose from a population of Mediterranean Arabs betwen 5 and 6 thousand years ago, and began their primary diasporic wanderings 3,000 years ago, with another massive spread about 2,000 years ago.  

Ethnic Jews (of whom there are many subtypes) have certain genetic traits, just like ethnic swedes or Italians or Koreans. These traits are the result of, just like all other groups' traits, thousands of years of interbreeding with similar people.  

An ethnic Jew might not be a religious Jew, though.  

Judaism as a religion is one of the three monotheistic relations that grew out of the eastern Mediterranean, and it's the oldest.  Judaism as a religion exists outside of ethnic boundaries, although there is a lot of overlap that is not seen in the other large religions (I do not consider Zoroastrianism to be large). Judaism can be practiced by ethnic Russians, Zulus, or any other group that wishes to convert. And of course there are different flavors of Judaism, just as there are different flavors of Christianity.
Hope that helps!