Friendship book
Friendship books (also known as "FBs" in their abbreviated form) are small booklets made by stapling paper together, or are sometimes just sheets or strips of paper. They are usually decorated and the person who starts the book writes their name and address as the first person sending the book. People often include a list of interests as well. The FB is then passed around from penpal to penpal, and can often also become a way for one to meet new penpals. Most people hope to see the book again once it is full so they add their return address to the back cover of the book too, or inscribe "Return to Sender" on it.