To Remain Behind, To Remain, To Stay Behind
intransitive verb, godan verb
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means remainder, so the verb vocab version is "to remainder." Let's make that sound better: to remain behind.
のこる
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: You decide to remain behind. Everyone else leaves, and you think you're alone. Then, someone knocks (のこ) on the door. Your heart jumps in your throat. They knock again.
私はここに残るよ。
I'll stay here.
クッキー、残っちゃったね。
The cookies got left, huh?
キャンプに行かずに家に残って、残っていたカレーを食べました。
I stayed home instead of going camping and ate the leftover curry.