What's the difference between a "fact" witness and an "expert" witness?

In a previous episode of the podcast attorney Bill Rogel mentioned the term "Fact Witness". One of our attentive listeners noticed and sent in this question, "Aren't ALL witnesses FACT witnesses?"In this solo episode partner Bill clarifies this somewhat baffling legal terminology of the courtroom, using examples from the hit movie My Cousin Vinny. What is the difference between fact and opinion in the eyes of the court?When is opinion allowable?And why was Mona Lisa Vito such a great witness to help Vinnie Gambini's case?