pen pal [ˈpen pæl] n. 笔友

英英解释（柯林斯词典）：

A pen pal is someone you write friendly letters to and receive letters from, although the two of you may never have met.

pen pal的特点：

• 笔友是指你给他写信，他也会给你写信的人（A pen pal is someone you write friendly letters to and receive letters from）
• 尽管你们俩可能从未见过面（ although the two of you may never have met.）

单词选自：

人教精通版小学《英语》