The judge may consider the witness's specialized (scientific, technical or other) opinion about evidence or about facts before the court within the expert's area of expertise, referred to as an "expert opinion". Expert witnesses may also deliver "expert evidence" within the area of their expertise.A fact witness is an individual, sometimes a clinical professional such as a forensic psychologist, who has personal knowledge of events pertaining to the case can testify as to things they have personally observed or witnessed.