Units field is used to display Units of Measure of certain item set up on the item record.
For more information about Multiple Units of Measure please visit following link: Multiple Units of Measure and to know more about how to set up Units of Measure the link: Setting Up Units of Measure.
If your business does not use Units of Measure and the Item column field Units is unnecessary for your transactions, you can remove it by disabling the Multiple Units of Measure feature under Setup > Company > Company Features > Items & Inventory subtab > Items section.
Once Units of Measure feature is enabled, you can no longer disable it without deleting all items in the system that have Units(s) of Measure.
Disabling Units of Measure will remove the following:
1. Units column field on transaction forms
2. Units Type, Stock Units, Purchase Units and Sale Units fields on item records
3. Units of Measure Center Link (List > Accounting > Units of Measure)