Other forms: pen pals
A pen pal is a friend who regularly writes you letters. Even though you've never met him, your pen pal may live in France and send you poems by Rimbaud.
Most pen pals get to know each other through the letters they exchange, and many of them live in different countries. Having a pen pal whose life is very different from yours can be fun and educational — in fact, you might first get a pen pal's name and address at school. Traditionally, pen pals write letters, although it's possible to do this via email too. In the UK, the term penfriend is more common.