ちなみに

ちなみに means "by the way", "incidentally": it adds a side detail to what has just been said, on the same subject. It starts a new sentence, and the information after it is extra – useful or interesting, but not the main point.

ちなみに or ところで

Both are "by the way" in English. ところで leaves the subject and opens a new one; ちなみに stays on the subject and adds to it.

• × 明日は祝日です。ちなみに、レポートはもう出しましたか → ところで、レポートはもう出しましたか

Asking a follow-up

In conversation, ちなみに also leads into a question about a detail of what the other person just said. It works in a meeting as well as with friends.