What is the excess TX fee?

Could you please clarify for me what the excess TX fee refers to in the context of cryptocurrency transactions? Is it a fee charged by the network for transactions that exceed a certain size or complexity? Or is it a penalty imposed by exchanges or wallets for exceeding a specified limit on transaction fees? Understanding the nature of this fee is crucial for me to properly manage my cryptocurrency transactions and avoid unnecessary costs. Could you elaborate on the specifics of this fee and how it may impact my transactions?