used in writing to represent the sound that people make when they are pausing or deciding what to say next

"What do you think of this jacket?" "Um, I don't know if I like the colour." “你觉得这件夹克怎么样？”“呃，我不知道是否喜欢这种颜色。”

"So what did you talk about?" "Um, I don't remember." “那么你们谈了些什么？”“嗯，我不记得了。”