Insurance
Also called: insurance policy, cover, coverage
Insurance is paying a small certain cost to avoid a large uncertain one, by pooling risk across many people. It works on the law of large numbers: one house fire is unpredictable, a million houses are a statistical problem. The rule that follows is counterintuitive but firm — insure what would ruin you, not what would merely annoy you, because every predictable small loss you insure is a loss plus the insurer's margin.