What is a fixed monthly rate?

Could you please explain to me what exactly is meant by a fixed monthly rate? I'm curious to understand how it differs from other types of interest rates or payment structures. Is it a guaranteed amount that remains constant regardless of market fluctuations or other factors? How does it impact the overall cost of a loan or financial product over time? I'm particularly interested in its applications in the world of cryptocurrency and finance, and how it might benefit or impact investors and borrowers alike.