The Vendor Name/Code in the item record is the field used to enter the item's name as called by your vendor which usually is in the form of part numbers and serials.
To allow you to make this field as a search option in transaction –
1. Populate the Vendor Name/Code in the item record. Note that this will not be found in item records that are not for purchase or resale.
2. Enter any vendor (or expected vendors) under the Purchasing/Inventory tab > Vendors subtab, not necessarily setting any as preferred.
3. Save the item record.
When you do this and create a transaction (example: Purchase Orders, Sales Orders, Bills, etc ) you can now opt to type in the vendor name/code instead of the item name/number under the Item column and it will still reference the same.
Item Name/Number: Item ABC
Vendor Name/Code: Part 1234
Vendor in Item Record = T
If you create a purchase order, and add a line item, you can either type in "abc" or "123" and both will show "Item ABC" as a search option.