To turn one's head or body to look behind or over one's shoulder; to turn around and look.
突然名前を呼ばれて振り返った。
I suddenly heard my name and turned around.
バスに乗ってから何度も窓の外を振り返った。
After getting on the bus I kept looking back out the window.
後ろで誰かが話している気がして、振り返った。
I thought someone was talking behind me, so I turned to look.
To look back on or recall the past; to reflect or reminisce (often used as 振り返ってみる — 'to look back and consider').
学生時代を振り返ると、もっと勉強すればよかったと思う。
Looking back on my student days, I think I should have studied more.
プロジェクトを振り返って、改善点を洗い出した。
We reviewed the project and identified points for improvement.
過去の失敗を振り返り、同じミスを繰り返さないようにした。
I reflected on past mistakes so I wouldn't repeat them.