Rule 190 “Proof” is the establishment by evidence of a requisite degree of belief concerning a fact in the mind of the trier of fact or the court.

When someone talks about "proof" in a California court case, they mean the evidence shown was strong enough to convince the judge or jury to believe a fact is true.

Different types of cases require different levels of convincing. For example, a criminal case requires the highest level of proof, meaning the jury must be convinced "beyond a reasonable doubt." A civil case uses a lower standard, where one side just needs to show their version of events is more likely true than not.

The key thing to understand is that proof is not just about having evidence. It is about whether that evidence actually convinced the decision maker. You can present evidence and still fail to prove your point if the judge or jury is not persuaded.