What is the network cost fee?

Could you please elaborate on what exactly is meant by the term "network cost fee" in the context of cryptocurrency transactions? Is it a fee that is charged by the blockchain network for processing and validating transactions? If so, how is this fee determined, and who ultimately pays for it? Additionally, are there any factors that can influence the amount of this fee, such as the size or complexity of the transaction, or the current congestion level of the network? Understanding the nuances of this fee is crucial for anyone looking to navigate the world of cryptocurrency transactions.