What is a fixed rate charge?

Excuse me, could you please explain what exactly is meant by a "fixed rate charge" in the world of finance and cryptocurrency? Is it a fee that remains constant regardless of the amount of the transaction or the market conditions? How does it differ from other types of charges, such as variable rate fees or percentage-based fees? Is it common practice for cryptocurrency exchanges and financial institutions to offer fixed rate charges, and if so, what are some of the benefits and drawbacks of this approach for both the service provider and the end-user?