This is the 8692nd most frequent Japanese word.
早口
Fast talking.
Here, '早口' describes the characteristic manner of speaking fast in the sentence.
彼はいつも早口で話します。
He always speaks in a fast manner.
In this context, '早口言葉' refers to tongue twisters, which are phrases focusing on fast speech for exercises.
早口言葉を練習して、発音が上手になりました。
By practicing tongue twisters, my pronunciation improved.
'早口' here indicates someone's fast spoken pace as an observable trait.