SharePoint Online is part of Microsoft Online Services.  It is a hosted environment for companies that would rather outsource their SharePoint data center than manage it themselves. 

SharePoint Online can be purchased as an individual service or as part of a suite of online services, which includes Exchange Online, Live Communications Server, and Live Meeting. 

If you are a virtual company, you can virtualize almost your entire data center in this way.

Two big announcements have occurred.

The first is that the largest company to date, GlaxoSmithKline, has signed up to move a portion, if not all, of their 100,000 employees to the Microsoft Online service.  They expect to save 30 percent of their related computing costs in this way.

The second announcement is that SharePoint Online is going global.  Until now, it has only been available in the United States.  19 countries  in Europe and Asia will be available for trial, beginning in April.

As found in:

Microsoft is expanding business online services, Seattle Times, Mar 2, 2009

GlaxoSmithkline deal highlight’s Microsoft’s overseas launch of hosted collaboration software, Computerworld, Mar 2, 2009