The SEIR model is a mathematical framework used to understand the spread of infectious diseases. It divides the population into four compartments: Susceptible, Exposed, Infectious, and Recovered. Individuals start as susceptible, then become exposed after contact with an infected person, followed by a period of being infectious, and finally recover, gaining immunity. This model helps public health officials predict how diseases like COVID-19 or influenza spread over time. By analyzing the transitions between these compartments, researchers can assess the impact of interventions, such as vaccination or social distancing, on controlling outbreaks.