Forensic:  Pertaining to or used in courts of law.

Engineering (the short version):  The application of the principles of physics and engineering sciences to create solutions to problems.

Expert (paraphrased):  A witness qualified by knowledge, skill, experience, training, or education, may testify in the form of an opinion if scientific, technical, or other specialized knowledge will assist the jury to understand the evidence or to determine a fact in issue.  Such testimony must be based upon sufficient facts or data, and be the product of reliable principles and methods that have been reliably applied to the facts of the case.