the possessive form of 'hair', indicating something belonging to or characteristic of the hair (e.g., 'the hair's texture').

髪の・毛の〜（所属・性質を表す所有格）

a contraction of 'hair is' (e.g., 'hair's getting long' = 'hair is getting long').

（'hair is'の短縮形）髪が〜である

a contraction of 'hair has' when used with a past participle (e.g., 'hair's turned grey' = 'hair has turned grey').

（'hair has'の短縮形）髪が〜した／〜している（現在完了の意味）