The term I²R refers to power loss in electrical systems due to resistance, where the current (I) squared is multiplied by the resistance (R). This equation effectively captures real power losses in resistive components. In contrast, I²Z includes impedance (Z), which incorporates both resistance and reactance, making it less suitable for evaluating power loss specifically, as it does not solely account for resistive losses and can misrepresent the actual energy dissipated as heat.