The phrase "special interest" refers to a specific topic, activity, or cause that someone is particularly focused on or passionate about. It usually involves a level of dedication and enthusiasm towards that particular area. Full definition
This will make political donations more transparent and helps to stop the influence of special interest groups in local government. (www2.erie.gov)
They're forming virtual communities of special interests in everything from celebrities to childhood vaccinations and attachment parenting. (psychotherapynetworker.org)
She is currently a staff veterinarian with special interests in surgery and shelter medicine. (phcanimalleague.com)