Google Docs is a web-based data storage service offered by Google which lets you share and edit files with collaborating people in real time. It combines different features of other service providers such as Writely and Spreadsheets.
I have used Google Docs all these years to share different documents to other people and it worked well enough. So I was just a little shocked when Google suddenly removed its Google Docs services and started offering Google Drive instead.
Well, in terms of service provision, I don't think that Google Drive has that much difference from Google Docs except for the name. But apparently, Google Drive, which is said to be an extension of Google Docs (if that may be the case, then where is Google Docs?), is a a file storage and sync service just like Dropbox.