Simplified example.
Say we are an insurance company, we have 10,000 policy-holders who paid $500 each for life insurance this year (that’s easiest to work with, property/casualty and multiple years have more wrinkles to 'em
So we have collected $5,000,000 in premium. Every time one of our insured policyholders dies, we pay out $100,000. We expect perhaps 20 deaths in a year, so we expect to pay out $2,000,000. If we have bad luck and get 25 deaths in that year, we’re still OK, we can afford to pay out $2,500,000. But there is a very small but still real unlucky chance that there would be 50 claims or more. In that case, we’re in trouble, we haven’t collected enough money to cover the losses.
So… We go to a reinsurance company. We figure that we can afford claims under $3,000,000 (say), so we insure ourselves (so to speak) against claims being higher than that. This “insurance on insurance” is called “reinsurance.” The chance of such event occurring is small, so the premiums are relatively small, but this protects our company against losses that we can’t afford.
The reinsurance company is collecting similar premiums from many, many insurance companies. During normal years, the reinsurance company does not ever have to make pay-outs. But in a year of some catastrophic claims, the resinurance company is on the hook.
Since the claims payouts are usually large (that’s why the insurance company wants to reinsure the loss), many reinsurance companies will often pool their risks together, through some sort of sharing arrangement.
That help?