N/file Module
File.description
Property Description: The description of a file. In the UI, the value of description displays in the Description field on the file record.
Type: string
Supported Script Types: Server-side scripts For more information, see SuiteScript 2.0 Script Types.
Module: N/file Module
Since: 2015.2
Search NetSuite - https://system.netsuite.com/app/help/helpcenter.nl?search=File.description

// Code Example 1

//Add additional code

//...

var fileObj = file.load({

    id: 'Images/myImageFile.jpg'

});

fileObj.description = 'my test file';

var fileId = fileObj.save();

//...

//Add additional code



//SOURCE: https://system.netsuite.com/app/help/helpcenter.nl?fid=section_4223862428.html