Worker's Compensation (colloquially known as worker's comp) is state-mandated indemnity insurance that covers lost income and/or medical expenses when injuries or illnesses happen at work. When an employee accepts worker's comp he also acknowledges that he is unable to sue his employer for negligence if the injury happened at work.
Workers' compensation laws were enacted to reduce the need for litigation. The first state law was passed in Maryland in 1902, and the first law covering federal employees was passed in 1906. By 1949, all states had enacted some kind of workers' compensation regime.
Today, however, 63 percent  of all disabling injuries and illnesses occur outside of work. For those injuries or illnesses, workers’ compensation does not apply. Only workers with disability insurance are covered.