A reference group is simply a group that you referred to for comparison . He said his party is a reference group , and it means that his party is one which others use to compare themselves with . They were my reference group and I based my judgment on everyone I saw, by the way they behaved throughout the day. . Eg . When I say that I am poor ,even if I am a multimillionaire , its because my reference group is 'the billionaire group '. If I were to used you as my reference group , then my work seems good , but If I used her as one , then my work is nothing since her standard is so high.

this seems like a scientific term. when measuring anything you need a reference, IE the distance from here to the moon is smaller than the distance from here to Jupiter. In political science they often take polls with varying questions and use a reference group to gauge the characteristics of the whole. https://www.boundless.com/marketing/textbooks/boundless-marketing-textbook/consumer-marketing-4/social-influences-on-the-consumer-decision-process-42/reference-groups-213-4121/