Final answer:
Expert sources refers to the opinions of people with acknowledged authority to support a message.
Step-by-step explanation:
When using the opinions of people with acknowledged authority to support a message, the type of sources you are using are expert sources. Expert sources are individuals who have a high level of knowledge, expertise, and credibility in a particular field or subject.
Expert sources can include scholars, scientists, professionals, and other recognized authorities in their respective fields. When citing expert sources, it is important to provide their credentials and qualifications to establish their authority.