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.
"Hey, um, can I go to the drug store?"
"I, um, went to the, um, bowling alley"
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"