Close friend; a very good and trusted friend (bosom friend).
小学校からの親友と今でも毎週会っている。
I still meet my childhood best friend from elementary school every week.
親友の結婚式でスピーチを頼まれた。
I was asked to give a speech at my close friend's wedding.
親友には何でも話せるから安心だ。
I feel at ease because I can tell my best friend anything.