Inside
In
noun
When the middle kanji is used as a word, it means inside. When you're in the middle of something, it means you're in that thing!
Since this word is made up of a single kanji, it uses the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word:
There's a sound coming from inside the wall. It sounds like a knock, knock, knock noise. You break down the wall, and there's some creepy dude standing inside. He is the knocker (なか).
はやく中に入ろう。
Let's go inside quickly.
このグループの中に、レイチェルはいますか?
Is Rachel in this group?
川の中からビキニの女が出てきた。
A woman in a bikini came out of the river.