General meaning:
* Expression: This is the most common translation and works in most situations.
Specific meanings:
* Expression artistique/littéraire: Artistic/literary expression
* Expression faciale: Facial expression
* Expression verbale: Verbal expression
* Expression mathématique: Mathematical expression
* Expression personnelle: Personal expression
Other possibilities:
* Manière de s'exprimer: Way of expressing oneself
* Formule: Formula (for mathematical or linguistic expressions)
* Phrase: Phrase (for short expressions)
It's always best to consider the context of the sentence to choose the most accurate translation.