Group 346 is the name of the shape. in earlier versions this name reflected
the position in the z order (front to back) and could change. In 2007 the
name is constant unless you decide to alter it.
Group 346 means :
1. It's a group!
2. It's the 346th thing added / changed on the slide.
The default name is less than useful but you can change it to something
useful like "my logo". by going to the selection pane.