To ensure that testimony is accurate and precise, expert witnesses frequently use nomenclature and terminology of their scientific disciplines without considering its comprehensibility to jurors. The role of the expert witness at a criminal trial is to serve as an instructor who provides the jury with the knowledge required to decide the issue to which the testimony is relevant. Since the jury will accept the instruction, information, and opinion of the expert in direct proportion to their confidence in his or her knowledge, familiarity with the subject, experience, and personal credibility, it is essential that communication be in basic terms readily understood by laypersons. Within the forensic sciences, it is important that the nomenclature of class and individual characteristics be adequately defined. 8 references.