For requests having the "Google Drive" cloud storage as strong requirement
Google Drive is a file storage and synchronization service provided by Google. It originally started as "Google Docs", and meanwhile includes cloud storage, file sharing and collaborative editing features. For users of Google+/Picasa, e.g. their private photos get stored here. For more details on the service itself, please refer to the linked Wikipedia article and information provided on the Google drive homepage itself.
When should this tag be used?
If the software you're looking for has Google Drive as a strong requirement (not just a "nice-to-have"), this tag is for you. Otherwise, you should rather refrain from using it. "Nice-to-haves" should be specified in the text of your post instead.