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