An "Epi" or epidemic refers to a sudden increase in the number of cases of a disease above what is normally expected in a specific area. This can affect a large number of people and can spread quickly, often requiring public health interventions. Epidemics can be caused by infectious agents like viruses or bacteria, and they can impact communities significantly. Epidemics can vary in scale and duration, with some lasting only a few weeks while others may persist for months or years. Examples include the flu, HIV/AIDS, and more recently, the COVID-19 pandemic, which began as an epidemic in Wuhan, China. Understanding the dynamics of epidemics is crucial for effective prevention and control measures.