What does the french slang tiz mean in English?

"Tiz" is not a common French slang term. It's possible you've heard a mispronounced word or that it's a very niche slang term.

Could you provide more context? For example:

* Where did you hear this word?

* What was the situation?

* Who said it?

With more information, I might be able to help you understand what "tiz" means in English.