Sampling in research is where a researcher only surveys some of the people in a population. The sample of people is representative of the overall population, but the size of the sample makes it easier and more cost effective to do the research.
Depending on the sampling method used, the sample may be representative or non-representative of the population. Non-probability sampling, for example, would not allow for inferences back to the
Probability sampling allows the results from research to be generalised and applied to the wider population which the sample resembles and represents. It also allows for a smaller number of people to be surveyed, where the population is too big to sample all its members.