Equivalent Series Resistance (ESR) refers to the internal resistance found in capacitors, which is present in series with the ideal capacitance. This resistance impacts the capacitor’s efficiency, especially at higher frequencies, by causing power losses and heat generation. High ESR can reduce a capacitor’s ability to filter out voltage ripple in power supplies, potentially leading to malfunction or reduced lifespan of electronic circuits. Monitoring ESR is crucial in applications like power electronics, where low ESR capacitors are preferred for better performance and reliability. ESR is typically measured in ohms and can increase as capacitors age or degrade.