A Federal Reserve publication notes that the shedding of unwanted inventories often accounts for a large portion

Question:

A Federal Reserve publication notes that "the shedding of unwanted inventories often accounts for a large portion of the decline in gross domestic product (GDP) during economic recessions." What does the author mean be "shedding of unwanted inventories"? What makes the inventories unwanted? Why would shedding inventories lead to a decline in GDP?