Preferred provider organization
A preferred provider organization is a subscription-based medical care arrangement. A membership allows a substantial discount below the regularly charged rates of the designated professionals partnered with the organization. Preferred provider organizations themselves earn money by charging an access fee to the insurance company for the use of their network (unlike the usual insurance with premiums and corresponding payments paid either in full or partially by the insurance provider to the medical doctor). They negotiate with providers to set fee schedules, and handle disputes between insurers and providers. PPOs can also contract with one another to strengthen their position in certain geographic areas without forming new relationships directly with providers. This will be mutually beneficial in theory, as be billed at a reduced rate when its insureds utilize the services of the "preferred" provider and the provider will see an increase in its business as almost all insureds in the organization will use only providers who are members. PPOs have gained popularity because, although they tend to have slightly higher premiums than HMOs and other more restrictive plans, they offer patients more flexibility overall.
Professional liability insurance
Professional liability insurance (PLI), also called professional indemnity insurance (PII) but more commonly known as errors & omissions (E&O) in the US, is a form of liability insurance which helps protect professional advice- and service-providing individuals and companies from bearing the full cost of defending against a negligence claim made by a client, and damages awarded in such a civil lawsuit. 
The coverage focuses on alleged failure to perform on the part of, financial loss caused by, and error or omission in the service or product sold by the policyholder. These are causes for legal action that would not be covered by a more general liability insurance policy which addresses more direct forms of harm. Professional liability insurance may take on different forms and names depending on the profession, especially medical and legal, and is sometimes required under contract by other businesses that are the beneficiaries of the advice or service.