Utilities are public organizations that provide services such as electricity, water, sewer and gas to local consumers. Utilities maintain the infrastructure to deliver those services. Each utility provides service within a specific location or service area. Anyone living within the service area is eligible to receive services from that utility company.
Unlike many other service-oriented businesses, utilities often function as monopolies, and may or may not be offered by the government directly. The reason a utility is approved to operate as a monopoly is that the infrastructure costs so much to build and maintain. The inability of multiple separate companies to provide the necessary infrastructure to serve customers isn't practical. Therefore, a single utility is allowed to operate without competition.
Yes, there are multiple types of utilities which can be classified based on the size of the service area they support and the particular service they provide. For example, a power and light utility company would probably not supply water service.