French phrase
C'est hors sujet.
Meaning
That's off topic.
When to use it
It indicates that a matter is unrelated to the agenda. It is formal and somewhat assertive in meetings.
Example dialogue
Je veux parler du budget des fêtes.
I want to talk about the party budget.
C'est hors sujet. Concentrons-nous sur le rapport.
That's off topic. Let's focus on the report.