Typically, the services allow HTTP access, and sometimes FTP access. Related services are content-displaying hosting services (i.e. video and image), virtual storage, and remote backup.
Document-sharing services allow users to share and collaborate on document files. These services originally targeted files such as PDFs, word processor documents, and spreadsheets.
However many remote file storage services are now aimed at allowing users to share and sychronize all types of files across all the devices they use.