The name of the organisation that maintains the codebase for the identically named OfficeSuite.
OpenOffice.org is an office suite, providing WordProcessor, SpreadSheet, presentation, DataBase and other tools. It is pretty good at importing MicrosoftOffice documents and can export to PDF natively. (The PDF page lists some good reasons why emailing PDF files around is better than Emailing word processor files around). It uses OpenDocument as its FileFormat, which is based on a well-designed XML structure rather than on an inscrutable binary format.
OpenOffice.org is Free and CrossPlatform, running under X11 on most Unices and Linux, as well as on MicrosoftWindows and MacOSX. You will find it on TheOpenCD, which is an easy way for MicrosoftWindows users to try OpenSource software without having to switch OperatingSystems up front.