A casual expression meaning 'exactly' or 'you got that right', used to strongly agree with someone's remark (common in conversation and on social media).
A: 今日寒すぎるよね。 B: それな、出かけたくない。
A: It's too cold today, right? B: Exactly — I don't want to go out.
あの店、サービス最高だよね。 — それな！
That shop has the best service, right? — Exactly!
SNSで友達の投稿を見て、心の中で『それな』とつぶやいた。
Seeing a friend's post on social media, I mentally said 'exactly'.
若者言葉なので、フォーマルな場では使わない方がいい（くだけた会話向け）。
Because it's youth slang, it's better not to use it in formal situations (suitable for casual conversation).