Can someone explain 'Title Commitment' in layman's terms?

I have found the def. on line but, can't understand what it means....I just found out that the place I make my mortgage pmts to - does not have my home registered with the county I live in. Also I requested a 'mortgage assignment' from the lien holder. (my mortgage was sold to the current lien holder 5-6 yrs ago.) they said that they don't have a 'mortgage assignment'........Something smells really fishy here.