Anyone who has spent any time at Microsoft knows the penchant demand for acronyms and jargon, it’s so prevalent that at one point someone created an internal glossary just so people could keep up with the alphabet soup. That project has since disappeared, I think simply because it couldn’t keep up!
The “MacBU” is the nick name we use to refer to our business unit at Microsoft. Our fully qualified name is the Macintosh Business Unit. We develop Office; Word, Excel, PowerPoint and Entourage, Remote Desktop Connection and Messenger. There are other Mac products at Microsoft, but they are not part of the MacBU. We say “MacBU” like “Mac boo” and often write “MBU” but say MacBU.
For completeness, we also use XL for Excel, Erage for Entourage, PPT for PowerPoint, RDC for Remote Desktop Connection and Msgr for Messenger. Every character counts, you know. Word doesn’t have an abbreviation, because it’s, well, Word. Yo. Now you can be all hip to the local lingo!