WWDC (World Wide Developer Conference) is Apple's yearly developer conference. The 2004 session descriptions are now available here, although the interesting sessions usually don't appear on the schedule until the first day when they make all their big announcements. If they follow the tradition of the last few years, they'll probably be announcing the details of Mac OS 10.4 (code named Merlot - what happened to the cat names?).
This will be the first one I've missed in years. I'll miss it, and all the excitement Steve Jobs generates. It's got a very different feel from Microsoft's PDC.