Definition - What does Expert Testimony mean?
Expert testimony is testimony from an expert who is presumed to be extremely knowledgeable about a relevant issue to the case. For example, a surgeon may provide expert testimony on a medical case where the plaintiff is suing their health insurance company. Expert witnesses are usually paid to give their testimonies.
Justipedia explains Expert Testimony
Expert testimony is most often used to clarify scientific or technical details that are related to civil and criminal cases. Experts are often called to testify in court because they possess technical knowledge that is critical to the case but that few other people may possess. For example, a psychologist may be called to give an expert testimony in a case that involves a criminally insane person. This testimony could provide critical insight into the case. Expert testimony is used by judes and juries to understand technical details related to the case.