As defined by USLegal.com, a lay testimony is a testimony based on the unique experiences and personal knowledge of a witness. A lay testimony is an individual's personal opinion and is the opposite of an expert testimony.
According to the Legal Information Institute of Cornell University, a lay testimony can only be accepted in a court of law if the witness's opinion is based on rational thinking, is helpful in some way to a portion of the case or the entire case, and is not supported by data or other technical knowledge.
Unlike witnesses providing expert testimony, witnesses giving a lay testimony do not need to be investigated before they appear in court. The Free Dictionary notes that courts must screen expert witnesses heavily to ensure that their definite opinions are not based on "common knowledge" and are reliable to help the jury make its decision.
The Boulder County Bar Association explains that expert witnesses are not as limited as lay witnesses in terms of what they can and cannot say in court. One powerful and definitive statement from an expert witness on the issue of a case often expedites the case altogether. Most cases profit more from expert testimony versus lay testimony.