'flag', but with four colored squares. Going by the video after the jump, the blue square appears to represent Windows, the red square Office, the green square Xbox (whose logo remains unchanged), and the yellow square ... something new, maybe?
For the last quarter of a century, Microsoft has used the "Pacman logo", as designed by Scott Baker in 1987. The slash between the o and s was supposed to represent the motion and speed of the company and its products. Microsoft chose to change the logo to "visually accentuate" a new beginning in the form of Windows 8, Windows Phone 8, the next version of Office – and maybe the next version of Xbox?
Take a look at an intro video from Microsoft below the break.