A small group whose characteristics accurately reflect those of the larger population from which it is drawn. This type of sample is often used as the beginning of a study or theory. For instance, if someone noted that a large amount of people with red hair lived in New York city, perhaps they would compare that data to other information about Chicago to try and find a logical explanation (a lot of the same people immigrated at the same time? large extended family? certain nationality that prefers something in New York City?).
Example: If approximately 15% of the United States’ population is of Hispanic descent, a sample of 100 Americans also ought to include around 15 Hispanic people to be representative.