Formal:
* Fin. (Most common, especially in academic settings)
* Final (Used in some cases, especially when space is limited)
Informal:
* Fnl. (Less common but still used)
Specific contexts:
* Exam: For "final exam," you might use "Final Exam" or "FE"
* Report: For "final report," you might use "Final Rep." or "FR"
It's important to consider your audience and the context when choosing an abbreviation. If you're unsure, it's always best to spell out the word "final" in full.