What is the slang meaning of kroner?

"Kroner" is the plural form of "krone," the currency of Denmark, Norway, and Iceland. It is not typically used as slang in any of those countries.

It's possible that you've heard "kroner" used in a slang context, but without more information, it's hard to tell what the meaning might be.

Could you provide more context or examples of how you heard the word used?