Part of Speech: Noun

Definition: a small bag that is carried over your shoulder and that is used for carrying clothes, books, etc.

Source: http://www.merriam-webster.com/dictionary/satchel

Meaning: I saw this word in the reading Who knows Brooklyn where it said  Manbeck reached into a satchel and pulled out his own latest volume, “Historic Photos of the Brooklyn Bridge,” which shipped recently.

This meant that Manbeck was carrying a bag with him in which he had the book he published.