Generally refers to a Pearson’s chi-square test, which is a statistical test used to determine how well a set of whole-number data matches expectations. Chi-square tests are often used when a test outcome takes the form of a number of different sorts of events. For example, a chi-square test might be used to determine how closely the sex ratio among the offspring of a particular mating match the expectations generated by Mendel’s laws or how closely the numbers rolled by a particular die match what we would expect if the die were fair. A chi-square test helps one figure out how likely a particular set of results are if a hypothesis (e.g., “Mendels laws apply” or “the die is fair”) were true.