These are fields that can have a custom label put on them and used for storing special information and filtering records by these. This is available for two fields in customers and two fields in inventory.
Customer Misc – This field value from the customer is also displayed as Notes within Sales Orders.
Customer User Type – Values entered for customers may also be used on Price Matrix records for defining special pricing for a particular customer group.
Inventory Misc – Not used outside of Inventory items
Inventory User Type – Not used outside of Inventory items