Say you want to give a survey to people from a population and assume that
people who volunteer to take the survey are not necessarily representative of the population ("volunteer bias") and
you don't actually know the underlying population demographics.
To be more specific, say you are trying to measure the gender balance in a certain population, and for example, the true balance is 50/50 (which you don't know), but the sample you get among survey takers is 55/45 (more females). Is there anything that can be done?