To enter or go into a place; when used about restricted areas it can mean trespass.
立ち入り禁止の区域には勝手に立ち入らないでください。
Please do not enter areas marked 'No entry' without permission.
庭に勝手に立ち入るのは失礼だ。
It's rude to enter someone's garden without permission.
古い校舎に立ち入ると危ないので入らないでください。
Please don't enter the old school building; it's dangerous.
To meddle in or interfere with someone else's affairs; to pry into matters that are not one's business.
君は関係ないことに立ち入るべきではない。
You should not meddle in matters that don't concern you.
友達の恋愛事情に立ち入ると、信頼を失うことがある。
If you pry into a friend's love life, you may lose their trust.
その問題にはあまり立ち入らない方がいいと助言した。
I advised them not to get too involved in that issue.
To go deeply into an issue; to investigate or delve further into a topic.
そのテーマには立ち入って詳しく調べる必要がある。
We need to delve into that topic and examine it in detail.
ここでは詳しい技術的な説明には立ち入らないで、概略だけ説明します。
I won't go into the detailed technical explanation here; I'll just outline it.
経済政策の歴史に立ち入ると議論が長引くことが多い。
Once you delve into the history of economic policy, discussions often become lengthy.