Definitions

1. noun

A narrow or vertical box-like compartment or recess, especially in a computer case or a book, used for storing small items such as cables or a USB flash drive.

“The computer case had a small sidebox to store my extra hard drive.”

2. noun

A small compartment or recess on the side of a page or a book, used to display or store a piece of information such as a table of contents or a map.

“The sidebox in the book contained a helpful map to the nearby cities.”