PlumWall is an online testimonial management system that allows credit unions to collect and display positive member reviews and stories on their website and through social media. It provides a way for credit unions to showcase the member experience and generate referrals without having to directly ask for reviews. The webinar presentation recommends starting by collecting employee reviews and stories, then obtaining member permission to share, and using the testimonials across various online and internal channels according to best practices. PlumWall is described as a powerful yet underused social media strategy that highlights the human impact of the credit union through members' own words.