This came up in a completely unrelated SE chat, with someone claiming that (unlike Christianity.SE being "about Christian doctrine and practice") Judaism.SE is "about Jewish culture".
My impression (perhaps incorrect) was that Judaism.SE had purely secular Jewish culture as out of scope, but I couldn't find anything explicitly stating so on Meta or in Help.
The best I found was : What topics are in- and out-of-scope on Mi Yodeya?
"On the other hand, questions unrelated to Judaism, even if they are about......"
".... Jews, Jewish history, and Israel "
... ... are generally off-topic.
Examples of "purely secular Jewish culture" would be (stolen from @msh's answer):
bagels and lox, borscht-belt comedians, Yiddish theater, kibbutz life, Fiddler on the Roof, and the Ladino language