What is Opinion Evidence?

Legal Definition
Opinion evidence refers to evidence of what the witness thinks, believes, or infers in regard to facts, as distinguished from personal knowledge of the facts themselves. In common law jurisdictions the general rule is that a witness is supposed to testify as to what was observed and not to give an opinion on what was observed. However, there are two exceptions to this rule: expert evidence and non-expert opinion given by laymen which people in their daily lives reach without conscious ratiocination.
-- Wikipedia
Legal Definition
Evidence of what the witness thinks, believes, or infers in regard to facts in dispute, as distinguished from his personal knowledge of the facts themselves ; not admissible except (under certain limitations) in the case of experts. See Lipscomb v. State, 75 Miss. 559, 23 South. 2l0.
-- Black's Law Dictionary
Legal Definition
a term applied to the evidence that is given by an expert witness.