"Contagious" refers to the ability of a disease to spread from one person to another. This can occur through direct contact, such as touching or kissing, or indirectly through surfaces or airborne particles. Common contagious diseases include the flu, common cold, and COVID-19. Infectious diseases are caused by pathogens like bacteria, viruses, fungi, or parasites. These pathogens can enter the body and multiply, leading to illness. Preventive measures, such as vaccination and good hygiene practices, help reduce the spread of contagious diseases and protect public health.