Learn in the textbookPopulation and Sampling
DefinitionIn a survey or analysis, the whole set of things whose characteristics you want to learn is called the population (母集団).
ExplanationWhat counts as the population depends on the purpose of the survey; to learn how long high school students in a certain city spend commuting, for instance, the population is every high school student in that city. The part chosen from the population to actually examine is called a sample. Results from the sample are the material for estimating the characteristics of the population.
AnalogyTo gauge how worn a library's whole collection is, every book in it is the population, and the few dozen you pick up and check are the sample.
Memory hookThe Japanese term 母集団 starts with 母, "mother": every sample is born from the population, so the character itself traces the relationship.