Voltage sag is a temporary reduction in voltage levels in an electrical system, often caused by sudden increases in load or short circuits. This drop in voltage can last from a few milliseconds to several seconds, affecting the performance of electrical devices and equipment. Common causes of voltage sag include motor startups, lightning strikes, and faults in power lines. While most electrical devices can tolerate brief sags, sensitive equipment like computers and medical devices may experience disruptions or malfunctions, leading to potential operational issues.