What does 伸び mean?
伸び is a Japanese noun meaning “growth; development” in English. It can also be translated as “stretching (one's body, e.g. when waking up), (ability to) spread (of paint, cream, etc.), elongation” depending on context. It is written as 伸び in kanji, のび in hiragana, and nobi in romaji. This word is part of JLPT N2 vocabulary.
Example sentence
もう髪を切ってもらってもいい時ですよ。大分伸び過ぎていますよ。
It's high time you had your hair cut, it's grown too long.