Inside
Within
noun, の adjective
The kanji and the word are exactly the same, so this means inside or within.
While 中 refers to the inside of something in a basic, positional sense, 内 tends to express a more abstract version of "inside," like 心の内を話す (express your inner feelings) or 温かい内に飲む (drink it while it's still warm).
It also carries an implied contrast with 外 (outside), so it's often used to talk about yourself or your group, like うちの犬 (our dog) or うちの会社 (the company I work for). In this case, it's almost always written in hiragana as うち — which is why we used it like that in these examples (but hey, now you know where that うち is coming from!).
Since this word is made up of a single kanji, it should use 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:
If someone were to peek inside your heart, they would say, "Ooh, cheese (うち)!" Most people's hearts are full of emotions and crippling insecurities and stuff, but yours has nothing but cheese within it. "Ooh, cheese… I love you so." That's all your heart's inner voice is ever saying.
このジャケット、内ポケットがいっぱいついてるよ。
This jacket has a lot of inside pockets.
このマスク、どっちが内でどっちが外か分かる？
Can you tell which side of this mask is the inside and which is the outside?
またその内、ごはんでも食べに行こうよ！
Let's go grab something to eat sometime!
彼はストレスで内にこもってしまった。
He withdrew into himself due to stress.
心の内をメッセージにしました。
I turned what was in my heart into a message.
An update is needed before you can continue but you have more than one WaniKani tab open.
Finish up what ever you are doing on the other tab(s), then close them to continue.
The update will complete automatically once the other tab(s) are closed.