noun: the process of making one's thoughts or feelings known
Crying can be a natural expression of sadness.
His face showed no expression, making it hard to tell what he was thinking.
If you're using the expression to talk behind someone's back, it means that the person talking is not saying good things about you. It's usually bad things.
noun: a word, phrase, or form of words used in speech or writing
It's a common expression in English to say 'time flies' when time passes quickly.
She used a strange expression I had never heard before.
The expression 'break the ice' means to start a conversation in a social setting.
