Definition
This idiom is used to indicate that someone does not possess a particular quality or have experience with a specific activity, suggesting a complete lack of understanding of its meaning or importance.
You say he's good at managing finances? He doesn't even know the meaning of the word "budget."
They criticize this policy for being unfair, but they do not know the meaning of the word "fairness."
Some people talk about "sacrifice" all day, but they really don't know the meaning of the word.