An entity seeking to transfer risk (an individual, corporation, or association of any type, etc.) becomes the 'insured' party once risk is assumed by an 'insurer', the insuring party, by means of a contract, called an insurance policy. Generally, an insurance contract includes, at a minimum, the following elements: identification of participating parties (the insurer, the insured, the beneficiaries), the premium, the period of coverage, the particular loss event covered, the amount of coverage (i.e., the amount to be paid to the insured or beneficiary in the event of a loss), and exclusions (events not covered). An insured is thus said to be "indemnified" against the loss covered in the policy.
Formal self-insurance is the deliberate decision to pay for otherwise insurable losses out of one's own money. This can be done on a formal basis by establishing a separate fund into which funds are deposited on a periodic basis, or by simply forgoing the purchase of available insurance and paying out-of-pocket. Self-insurance is usually used to pay for high-frequency, low-severity losses. Such losses, if covered by conventional insurance, mean having to pay a premium that includes loadings for the company's general expenses, cost of putting the policy on the books, acquisition expenses, premium taxes, and contingencies. While this is true for all insurance, for small, frequent losses the transaction costs may exceed the benefit of volatility reduction that insurance otherwise affords.
Social insurance can be many things to many people in many countries. But a summary of its essence is that it is a collection of insurance coverages (including components of life insurance, disability income insurance, unemployment insurance, health insurance, and others), plus retirement savings, that requires participation by all citizens. By forcing everyone in society to be a policyholder and pay premiums, it ensures that everyone can become a claimant when or if he/she needs to. Along the way, this inevitably becomes related to other concepts such as the justice system and the welfare state. This is a large, complicated topic that engenders tremendous debate, which can be further studied in the following articles (and others):