insertion; letter drop
sending to a prisoner; thing sent to a prisoner
supply of provisions, refreshments, etc. to someone carrying out a task
差し入れ、ありがとう！
Thanks for the treats!
同僚が徹夜組に差し入れをした。
A colleague brought treats to the team working all night.
親が受験勉強中の子供たちに差し入れを持ってきた。
The parent brought treats for the children studying for exams late into the night.