Definition of "Expression" :

noun: the act of forcing something out by squeezing or pressing

"The expression of milk from her breast."

noun: the feelings expressed on a person's face

"A sad expression."

noun: a group of words that form a constituent of a sentence and are considered as a single unit

noun: a group of symbols that make a mathematical statement

noun: expression without words

"Tears are an expression of grief."

noun: the style of expressing yourself

"His manner of expression showed how much he cared."

noun: the communication (in speech or writing) of your beliefs or opinions

"Expressions of good will."

noun: a word or phrase that particular people use in particular situations

"Pardon the expression."

noun: (genetics) the process of expressing a gene