Web services and SuiteScript code need to reference internal IDs in order to uniquely identify objects,So it is recommended that you enable this preference whenever you are working with Web services or SuiteScript.
To enable this preference
Go to Home>Set Preference and Check Show internal IDS check box to enable this preference
You can view the internal ID for a field by clicking on that field’s label to open the field level help popup window.
You can view the internal ID for a record or a custom field in an Internal ID column that displays on a list or search results page for that type of record or custom field