Adjustment Types are used for both positive and negative adjustments. They give you a brief description of the reason for the adjustment, such as "Professional Courtesy" or "Bounced Check Fee".
To create a new adjustment type, go to References and select Adjustment Types in the sidebar. Click the green plus button to create a new record, and enter the adjustment type you'd like to add.
After entering the information, save the new record by going up to the Edit menu and choosing Save Record, or using the Command-S keyboard shortcut.