What is referred to as any person or entity supplied with electric service under a contract?

The term that describes any person or entity supplied with electric service under a contract is "Customer." In the context of electrical utilities and power distribution, a customer is typically someone or an organization that engages in a contractual agreement to receive electricity. This term encompasses residential, commercial, and industrial entities that rely on electric service for their operations or needs.

The choice of "Customer" is particularly appropriate because it indicates an ongoing relationship defined by service provision and payment obligations specified in the contract. This relationship conveys that the entity is not just a recipient of electric service but is also engaged in a transactional agreement which may outline various terms and conditions, including pricing, service levels, and usage expectations.

Other options like "Client," "Consumer," and "End User" do not fully capture the contractual aspect of the relationship in the same way. While these terms may refer to individuals or groups needing electricity, they lack the formal acknowledgment of a service agreement that defines a customer's relationship with the utility provider. Thus, "Customer" is the most accurate choice when discussing entities supplied with electric service under a contract.