everyone and their mum字面意思每个人和他们的妈妈，引申为大多数人，很多人。

【例句】
Everyone and their mum seems to be going to concert tonight.
大多数人都去了那个演唱会。

Everyone and their mum is going on a vacation, but I have to work.
大家都要休假了，可我还得工作。