Sampling is a statistical process in which a smaller subset of people from an entire population is selected to form a sample. The chosen people should share characteristics that are representative of the overall population. Yet, the sampling could be used to manipulate the end result, when the one who is choosing the sample, samples a specific group of people that shares an opinion that the author of the survey wants to receive.
The results obtained on studying a sample can therefore be generalized as being applicable to the whole population as well.