Snowball sampling is a non-probability sampling technique often used in research when the population is hard to access. In this method, existing study subjects recruit future subjects from their acquaintances, creating a "snowball" effect. This approach is particularly useful for studying specific groups, such as marginalized communities or hidden populations. Researchers begin with a small group of participants and ask them to refer others who meet the study criteria. As more participants are recruited, the sample size grows, allowing researchers to gather data from a broader network. However, this method may introduce bias, as the sample may not represent the entire population.