An insider is someone inside a group, a company, or an organisation, so they know things that people on the outside do not. A hospital insider may know how decisions are really made. A political insider knows what is happening behind the public talk.

An insider is someone inside a group, a company, or an organisationInsider是身處某個團體、公司或組織內部的人，so they know things that people on the outside do not所以他們知道外面的人不知道的事情。A hospital insider may know how decisions are really madeA hospital insider可能知道決定其實是怎麼做出來的。A political insider knows what is happening behind the public talkA political insider知道公開談話背後正在發生什麼事。

Though actually, the word is not only about secrets. Sometimes it just means “one of us”: a person who belongs to a scene, a sport, or a job.

Though actually不過其實，the word is not only about secrets這個字不只是關於秘密。Sometimes it just means "one of us"有時候它就只是『自己人』的意思：a person who belongs to a scene, a sport, or a job一個屬於某個圈子、某項運動，或某份工作的人。

The darker use is using private company news to buy or sell shares — in English, insider trading; that is against the law.

The darker use is using private company news to buy or sell shares比較負面的用法是利用公司內部的消息來買賣股票 — in English, insider trading英文叫insider trading；that is against the law那是違法的。

Newspapers like the word because it suggests special knowledge. It is common in news and business English. In casual talk, people also call someone an insider when they are really in a small circle.

Newspapers like the word because it suggests special knowledge報紙喜歡用這個字，因為它給人一種擁有特殊消息的感覺。It is common in news and business English它在新聞和商業英文裡很常見。In casual talk在輕鬆的談話裡，people also call someone an insider when they are really in a small circle當某人真的屬於一個小圈子時，人們也會叫他insider。