The terms "contagious" and "infectious" refer to how diseases are transmitted. Diseases considered contagious are spread through direct contact, while infectious diseases can spread through air or water. Understanding this distinction is important for clarity in discussions about health and disease prevention.

Additionally, both words can have figurative meanings. For example, "contagious laughter" conveys the idea that laughter can spread from one person to another, much like an illness. Similarly, "infectious enthusiasm" suggests that someone's excitement can easily influence others. In this context, either term is acceptable, highlighting how ideas and emotions can also spread among people.