What is a transfer fee?

Excuse me, could you please explain what exactly a transfer fee is in the context of cryptocurrency and finance? I understand it's some sort of charge, but I'm not entirely clear on the specifics. Is it a fee that's levied when funds are moved from one wallet or account to another? If so, what determines the amount of the fee, and who collects it? Also, are there any ways to minimize or avoid transfer fees altogether? I'd appreciate any clarification you can provide.