A standalone script is any script that is not bound to a Google Sheets, Docs, Slides, or Forms file. These scripts appear among your files in Google Drive.
Creating a standalone script
The easiest way to create a standalone script is to visit
and at the top left, click New project.
You can also create standalone scripts from Google Drive. Go to Google Drive and click New > More > Google Apps Script.
Running a standalone script
To run a function from the script editor, at the top, select the name of the function you want to execute and click Run.
Using a standalone script
Many standalone scripts are utility scripts — for example, to search your Google Drive for old files whose name contains "untitled" so that you can delete them.