Equivalent circuit refers to the simplified schematic representation of a more complex electrical circuit, which has the same behavior and output characteristics. The term 'equivalent circuit' can be used interchangeably with other related terms, such as simplified circuit, model circuit, or substitute circuit. A similar term is 'circuit model,' which refers to a mathematical model of a circuit that can be used to analyze and predict its behavior. Other related terms include 'transformed circuit,' 'ideal circuit,' and 'approximate circuit.' Whatever term is used, the main purpose is to simplify a complex circuit by reducing it to a simpler, more manageable form that can be analyzed and manipulated more easily.