What is fee margin?

Excuse me, could you please clarify what exactly is meant by the term "fee margin"? I understand it has something to do with finances and cryptocurrency, but I'm not entirely sure how it fits into the bigger picture. Is it a type of profit that's generated from transactions or services? And how does it differ from other types of margins or fees in the industry? I'd appreciate any insight you can provide to help me better understand this concept.