"Long hair" is used to describe hair that is longer than usual. This phrase is of Engpsh origin and is used in both formal and informal contexts. Here are some example sentences in Engpsh and their translations in Chinese:

She always wears her long hair in a ponytail.
她总是把她的长头发扎成马尾。

He grew out his hair because he wanted a change.
他留长头发是因为他想换个发型。

The model on the runway had long, curly hair.
走秀的模特有着卷曲的长头发。