Cloud storage is a model where user data is stored virtually in pools hosted by third parties rather than locally on users' computers. It offers advantages like flexibility to access files from any device, automatic backups, and pay-as-you-go pricing. Popular cloud storage services discussed in the document include Google Drive, YouTube, Just Cloud, Scribd, Picasa, and SlideShare. Each service offers its own features for file sharing, video hosting, backup, document sharing, photo organization, and presentation sharing over the internet.