A branching process is a mathematical model used to describe the growth and evolution of populations, where each individual can produce a certain number of offspring. This process is often represented as a tree structure, where each branch represents an individual and its descendants. The model helps in understanding how populations change over time, including extinction probabilities and growth rates. In a branching process, the offspring of each individual can vary, leading to different outcomes for the population. This concept is widely applied in fields such as biology, ecology, and epidemiology to study phenomena like the spread of diseases or the survival of species in changing environments.