ごめんなさい。

Gomennasai.

I’m sorry.

Word for word

“Please forgive me.”

Politeness: Neutral

Fixed expression that suits almost everyone, with no politeness marker to adjust.

When you would say it

A sincere apology to friends, family, and people you know.

Worth knowing

To strangers and at work, すみません or 申し訳ありません sound more fitting.