Infectious disease refers to illnesses caused by harmful microorganisms, such as bacteria, viruses, fungi, or parasites. These pathogens can invade the body, multiply, and disrupt normal bodily functions, leading to various health issues. Common examples include the flu, common cold, and COVID-19. Infectious diseases can spread from person to person, through contaminated food or water, or via insect bites. Preventive measures, such as vaccinations, good hygiene practices, and proper sanitation, are essential in controlling the spread of these diseases. Understanding how they transmit helps in reducing outbreaks and protecting public health.