What is an item master?

I've started working on an app that someone else (who is not available to ask questions) created and it uses an "item master" table. I've never used an item master table before -- can someone give me a good explanation of item master? I'm assuming that it's used to identify each entity in the database but I need a clearer understanding of how these things are supposed to work, their purpose/function, etc.
jwdc29@hotmail.com