What are metaclasses in Python and when should you use them?

I'm learning advanced Python concepts and recently came across metaclasses. I understand that classes are objects in Python, but I'm confused about what metaclasses are and why they're needed.

Can someone explain what metaclasses are, how they work, and when they should be used in real-world applications? I'd also like to understand how metaclasses differ from regular classes and decorators, along with a simple example demonstrating their purpose.