Microsoft Office is a suite of desktop applications for the Microsoft Windows and Mac OS X operating systems.
Early versions of Office included Microsoft Word (word processing), Microsoft Excel (spreadsheet) and Microsoft PowerPoint (presentation graphics). Other applications have since been added.
Applications share a range of features, including a common spell checker, OLE data integration and the Microsoft Visual Basic for Applications scripting language. The current versions are Office 2010 for Windows and Office 2011 for Mac OS X. Office 2013 is scheduled for release at the end of 2012.
Microsoft Office is currently the world’s most popular office suite and now has more than a billion users. Many other office suites, including Open Office and LibreOffice, have a similar look-and-feel to Microsoft Office and support the same file formats, allowing them to read and write Office files.
Microsoft Office is not currently available for mobile devices, but Microsoft have announced plans to produce a mobile version. Compatible applications, such as Polaris Office and Documents to Go are available for Android devices.
You can get more information from the Wikipedia article on Microsoft Office.
Instructions on how to install Microsoft Office 2010 can be found at: