Which class of circuit does not specifically mention a power source in its definition?

The correct answer is "General" because, in the context of fire alarm systems, the term "General" refers to a category of circuits that do not have a specific definition including particular requirements regarding a power source. This classification is broader and encompasses various types of circuits that may operate under different conditions.

In contrast, Class 1, Class 2, and Class 3 circuits all have specific definitions that include stipulations about power sources. For example, Class 1 circuits are typically associated with circuits that can be powered from any source, including both fire alarm control panels and external power supplies, and they often involve specific safety requirements to minimize risks. Class 2 and Class 3 circuits also have defined parameters in terms of power and limitations on wiring, which include the source of power as a fundamental part of their definitions. Therefore, the term "General" stands out because it lacks these specific references, making it the correct choice for circuits that do not explicitly mention a power source.