〜間(あいだ) / 〜間(あいだ)に

while / during

Marks a period of time. With 間(あいだ), something goes on for the whole period; with 間(あいだ)に, something happens at some point within it.

Readings

How to form it

Put a plain verb (often ている) or い-adjective before 間(あいだ): 日本(にほん)にいる間(あいだ), 若(わか)い間(あいだ).
Nouns take の and な-adjectives take な: 夏休(なつやす)みの間(あいだ), 暇(ひま)な間(あいだ).
With 間(あいだ), the main clause lasts the whole period: 待(ま)っている間(あいだ)、本(ほん)を読(よ)んでいた (I read the whole time I was waiting).
With 間(あいだ)に, the main event happens once inside it: 寝(ね)ている間(あいだ)に、電話(でんわ)があった (there was a call while I was asleep).

日本(にほん)にいる間(あいだ)、たくさん旅行(りょこう)しました。

I travelled a lot while I was in Japan.

寝(ね)ている間(あいだ)に、電話(でんわ)がありました。

Someone called while I was asleep.

The two halves can have different subjects: 母(はは)が出(で)かけている間(あいだ)に、部屋(へや)を掃除(そうじ)した (I cleaned my room while my mother was out).

Leaving out に for a one-time event inside the period. Say 寝(ね)ている間(あいだ)に電話(でんわ)があった.

〜ながらwhile doing
One person doing two actions at once.
〜うちにwhile (still) / before
"While" a state lasts, often with the sense of before it changes.