This document defines key terms related to sampling methods in statistics. It explains that a population is the entire group being studied, while a sample is a subset of the population that is surveyed to make inferences. There are different types of samples, including random samples where each member has an equal chance of being selected, stratified samples which are selected randomly from subgroups, and convenience samples which are easiest to reach. The document also notes that biased samples do not accurately represent the full population.