to go to bed

I usually turn in at about midnight. 我通常午夜左右才上床睡觉。

to take a criminal to the police, or to go to them yourself to admit a crime

The hit-and-run driver turned himself in to the police the day after the accident. 事故发生后的第二天，这名交通肇事逃逸的司机向警方自首了。

to return something to an organization or a person in authority

Please turn your old parking permits in at the end of the week. 请于本周末交回旧的停车证。

Thousands of weapons were turned in during the national gun amnesty. 在全国枪械特赦期内，人们上交了数千件武器。

to produce results, usually good results

Both companies turn in pretax profits of over 5.5 million annually. 两家公司每年获得超过550万的税前利润。