A single-issue group is an organization that focuses exclusively on one specific area of public policy, advocacy, or concern, often mobilizing people to influence legislation or political action related to that issue. These groups can play a significant role in shaping policy outcomes by concentrating their efforts and resources on a single cause, such as environmental protection, gun rights, or reproductive rights. Their focused approach allows them to be highly effective in rallying support and mobilizing voters around their specific agendas.