What does onus to prove mean?

Excuse me, could you please clarify the meaning of the phrase "onus to prove"? I understand it's related to the burden of proof in some legal or argumentative context, but I'd like to have a more detailed explanation. Specifically, how does it differ from the general idea of proof and what are some real-world examples where this concept might be applied? Additionally, are there any specific industries or fields, such as cryptocurrency or finance, where the onus to prove holds particular significance? Thank you for your time and consideration.