Google Drive is a cloud storage platform operated by Google and used for many of its services. Google Drive was announced in early 2012 as a replacement for the previously document-centric Google Docs, and was focused to be a direct competitor to the other cloud storage providers such as Dropbox and Box. Originally launching as a stand-alone data silo with 5GB of free storage, Google Drive has expanded to be the storage backbone for Google Docs, Gmail and other Google services, offering up 15GB of total storage across different apps.
Google Drive has apps for mobile platforms, as well as sync clients for desktop operating systems that keep all of your files in sync across every device where you're signed in. Google Drive is also deeply integrated into the Chrome OS platform, making it easy to keep all of your files of any size up-to-date across Chromebooks as well. Those who buy a new Chromebook are given 100GB of Google Drive storage for free for two years, many phone manufacturers offer up a free 50GB of free storage, and purchasing additional storage is extremely cheap compared to other providers.
In an attempt to further define its identity as a purely storage solution, Google Docs, Sheets and Presentations were broken out from the core Google Drive app on mobile in April 2014. This meant that going forward, if you wanted to edit documents on mobile you'd need the separate Docs, Sheets and Presentations apps, and you could only view documents via Drive. This has helped clear some of the confusion around the difference between Google Drive and Google Docs.