ONLamp has a pretty good article about the differences between ODF and OOXML. ODF (Open Document Format) and OOXML (Office Open XML) are both XML-based file formats which can be used to store word-processing documents, spreadsheets, etc. There is fierce competition for adoption between these two formats, notably in the arena of long-term government document storage. This competition is controversial for a number of reasons, including the fact that OOXML is a Microsoft product.
A google search for 'OOXML "men in black"' turns up quite a few hits regarding allegations of Microsoft lobbyists and lawyers trying to sway state legistatures (like Florida) toward OOXML.