The simple approach is that Cloud Computing is where you are storing information on the web, rather than on your hard drive or a memory stick, and you do not necessarily know or care exactly where it is stored. So examples would be
- GMail but not Outlook
- Google Documents but not MS Word or Excel
- Flickr and other photo storage sites
- etc
Word of caution. If you are storing business information in this way, you ought to find out where the data is physically stored as any legal issues with the data could need to be handled under the laws of that country.