The siemens (S) is an SI derived unit of electrical conductance. It measures the degree to which a material or component allows electric current to flow, defined as the reciprocal of electrical resistance. Since resistance is measured in ohms ($\Omega$), the siemens is dimensionally equivalent to $\text{ohm}^{-1}$. In the context of electrical circuits, conductance relates the current passing through a conductor to the applied voltage. Because it is a fundamental unit in electrical engineering and physics, it is used to quantify the efficiency of current pathways and the overall conductive capability of materials and devices.