The watt (W) is the standard international unit of power, which is fundamentally defined as the rate at which energy is transferred, used, or converted. In electrical circuits, it measures the rate at which electrical work is performed. Mathematically, one watt is equivalent to one joule of energy expended over a duration of one second. Power can be calculated by multiplying voltage by current; therefore, a watt quantifies the relationship between the electrical potential difference and the flow of charge through a circuit, making it a crucial metric for assessing the capacity and efficiency of energy systems.