あいだに = aidani

Credit : Maggie Sensei

★間に = あいだに = aidani 

*How to form:

* noun + の ( = no) +  間に ( aida ni)

Ex. 休み時間の間に

= yasumi jikan no aida ni

= During the break 

* verb (dictionary form / progressive form ている ( = teiru) ) / +   間に ( aida ni)

Ex. マギーがいる間に／いない間に

= Maggie ga iru aida ni / inai aida ni

= While Maggie is here / is gone 

Ex. 寝ている間に

= Nete iru aida ni

= While sleeping

*How to use: ~ 間に ( = aida ni )  ~ 

(1) While / During (A),  you want to do something/ You have to do something.

→You choose that time period to do something. / You do something intentionally during the time period.

Let’s compare the following sentences:

Ex. 母がいない間、ゲームで遊んでいた。

= Haga ga inai aida, geemu de ason de ita.

= While my mother was away, I had been playing the game. 

→The whole time when my mother was away, I was playing the game.

Ex. 母がいない間にゲームで遊んだ。

= Haha ga inai aida ni geemu de ason da.

= While my mom was away, I played the game.

→I would get in trouble if my mother found out I was playing the game too much so I took out the game as soon as my mom went out and played the game until she came back.

So you use 間に ( = aida ni) when you take advantage of the time to do something.

Ex. 休みの間に漢字を200個覚えた。

= Yasumi no aida ni kanji wo nihyakko oboeta.

= I learned 200 kanji during the holidays.

Ex. 親が出かけている間に部屋の片付けをしないといけない。

= Oyaga dekakete iru aida ni heya no katazuke wo shinai to ikenai.

= I have to clean up my room when my parents are away.

Ex. マギー先生が寝ている間におやつをとった人は誰ですか？

= Maggie sensei ga nete iru aida ni oyatsu wo totta hito wa dare desu ka?

= Who took Maggie Sensei’s snack while she was sleeping?

Ex. 彼を待っている間にジュースを買いに行った。

= Kare wo matte iru aida ni juusu wo kaini itta.

= While I was waiting for him I went to buy juice.

Ex. 父がまだ元気な間に富士山を見せてあげたい。

= Chichi ga mada genki na aida ni fujisan wo misete agetai.

= I’d love to show my dad Mt.Fuji while he is still healthy and energetic.

Ex. 若い間にいろいろな国に旅行をしておいた方がいいよ。

= Wakai aida ni iroirona kuni ni ryokou wo shite oita hou ga ii.

= You should travel as much as possible while you are young.

Another usage is 

(2) While / During (A),  someone do/did something/ something happened.

So in this usage, you don’t control your action. You just state what happened during the time period. 

Ex. 留守をしている間に宅急便が来た。

= Rusu wo shite iru aida ni takkyuubin ga kita.

= While I was away, the delivery service came.

Note: You can’t say

留守をしている間、宅急便が来た。(incorrect)

= Rusu wo shite iru aida, takkyuubin ga kita.

Because as we explained above, 宅急便が来た ( = takkyuubin ga kita) is just one time action. 

Ex. 彼は知らない間に出かけてしまった。

= Kare wa shiranai aida ni dekakete shimatta.

= I was gone before he realized it.

(* You can also say 知らぬ間に ( = shiranu mani ) )

Ex. 喫茶店でお茶を飲んでいる間に雨がやんでいた。

= Kissaten de ocha wo nonde iru aida ni ame ga  yande ita.

= It stopped raining while I was having a cup of tea at the coffee shop.

You can also indicate certain time period

Ex. ここ２ヶ月の間に随分日本語が上達してきた。

= Koko nikagetsu no aida ni zuibun nihongo ga joutatsu shite kita.