Definitions
1.nounA service performed for the public good, especially by a nonprofit organization but sometimes also provided by a for-profit enterprise or a trade association."This has been a public service announcement from the Advertising Council."
2.nounThe business of providing an important commodity (such as water, electricity, or gas) or a service (such as public transportation, communications, or community health centers) to the general public, often in the form of a publicly or privately owned public utility or a publicly funded nonprofit organization (e.g. community health center, public hospital). (Fire departments, police, courts, public schools, military, e.g., are considered part of the public sector, but not usually called public services.)
3.nounGovernment employment, especially in the civil service.
4.nounA service such as health care, transport, or waste removal usually provided by the government to the general public; often called a public sector organization in US English.