What is the purpose of the FEI number?

Excuse me, could you please elaborate on the purpose of the FEI number? I understand it's associated with financial entities and possibly has some regulatory significance, but I'm not entirely clear on its exact function and why it's important. Could you please provide a concise explanation of what the FEI number stands for, its purpose, and how it's used in the finance industry? Thank you in advance for your clarification.