(Not) Kosher

What does the expression “not kosher mean?

Definition: improper, wrong, not OK

Example: Janice borrowed $75 from me last week, and she still hasn’t given it back. That’s not kosher.

Note: The word “kosher” refers to Jewish dietary laws. But in the U.S. the term is used for things other than food, and used by non-Jews, very often.