Broader impacts means that a research group must take an interdisciplinary and transdisciplinary approach to their project. Interdisciplinary (ID) approaches integrate knowledge across the disciples. An example of this is a biologist discussing with a economist or a chemist. Transdisciplinary (TD) approaches seek to bring non-academics into the knowledge production process. Transdisciplinary studies focus on the co-production of knowledge from many different areas of our society. These terms can become confusing when you consider the subtle (but important!) differences between multidisciplinary, narrow interdisciplinarity, wide interdisciplinarity and the other types of ID. Julie Klein, a professor of the Humanities and a scholar of interdisciplinarity, wrote a great article explaining the taxonomy of interdisciplinarity. See her article here.
An example of transdisciplinarity would be a biologist meeting with some of the locals in his city to see what types of research the society is interested in. Another example would be a humanist and a scientist working together to discover the best ways to approach scientific research.
Of course, how you actually do these two tasks is something of a riddle. ID/TD are new concepts and integrating them into the disciplinary mind-set of the institutions of higher education is not easy. It will take some time to show the importance of these types of studies, but it is clear that funding for scientific research is becoming more and more focused on the broader impacts of a project. It will be necessary to turn to interdisciplinary/transdisciplinary studies so that research groups can understand the broader impacts of their work.