An item master is a record of all the key information about a particular item of inventory. This could include the date of manufacture, a short description of the inventory item, its dimensions (size, weight etc.), its cost, as well as information about current stock levels.
Item master data covers all the information about the inventory currently in a company's possession. Greater detail and granularity in the item master data gives the company greater potential for gleaning useful trends and information from it; such as what are the most commonly procured types of items, what sizes move the quickest, and what kinds of inventory are not as coveted.