colloquial expression meaning 'come to think of it' or 'that reminds me', used to recall or introduce a related topic
そういや昨日、彼から連絡があったよ。
Come to think of it, I heard from him yesterday.
A: 新しい店行った？ B: そういやまだ行ってないな。
A: Have you been to the new shop? B: Now that you mention it, I haven't yet.
そういや、明日は会議があったね。準備しないと。
That reminds me, there's a meeting tomorrow. I need to prepare.