Onus probandi
the burden of proof
Where the phrase comes from
The rule that the person who asserts a fact has to prove it. Criminal cases use a higher standard than civil cases.
What lawyers are pointing at
The onus answers two questions: who must bring the evidence, and how sure the fact-finder must be. In a criminal trial the prosecution carries the onus beyond reasonable doubt. In a civil claim the usual standard is the balance of probabilities. The onus can shift on a particular issue when a statute or a presumption says so. Volume of speech does not carry it. A repeated claim is not proof.
The same shape in code
The person who says a deploy is safe carries the onus. The artifact is a probe result, a checksum, or a row count, produced before the claim. A sentence in chat that says 'trust me, I tested it' leaves the onus where it started.
A concrete picture
A neighbor says your tree root broke their pipe. They have to show the break and the cause. You do not have to prove that every other possible cause is impossible before they have shown theirs.