Item Master Item Types in Oracle Inventory

Item Master Item Types are Lookup Type which is held in the table fnd_common_lookups. Use the below SQL Query to see the entries: 

SELECT lookup_type, lookup_code, meaning
FROM fnd_common_lookups 
WHERE lookup_type = 'ITEM_TYPE' 

order by lookup_type, lookup_code; 

Join Condition:- 
mtl_system_items_b.item_type = fnd_common_lookups.lookup_code