[exclamation] - a written representation of a sound that people make when they are pausing or deciding what to say next"What do you think of this jacket?" "I'm not sure - um, I don't know if I like the colour.""So what did you talk about?" "Um, I don't remember, I suppose work mainly."Um, I can't seem to get this machine to work.
UM
Meaning of UM in English
Cambridge English vocab. Кембриджский английский словарь. 2012