n.

1. 表达；表示[U][C][（+of）]
   I sent them flowers as an expression of thanks.

   我给他们送去鲜花表示感谢。

   the free expression of ideas

   自由发表意见

2. 表情；脸色；声调[C][U]
   There was no expression on her face.

   她脸上毫无表情。

3. 表现力[U]
4. 措辞；词句[C]
   "Shut up" is not a polite expression.

   “住口”不是有礼貌的话。

5. 榨出，挤压[U]
6. 【数】式；符号[C]

n.

1. the action of expressing something.
2. a look on someone's face that conveys a particular emotion.
3. a word or phrase expressing an idea.
4. Mathematics  a collection of symbols that jointly express a quantity.