If you really don't know what to say and/or you are in the middle of either making up something or trying to remember what you about to say, this vocal contortion is emitted.
Arabic word meaning mother. When used as a prefex it means "mother of". Usually as a mark of respect to the woman.
Mother calling her young son:"Sami, come and take this dish of desserts to our neighbour Um Ali and thank her for her help with the shopping the other day"