Windows Blue is definitely not Windows 9 but it's also not just a 'feature pack' update for Windows 8. Windows Blue is an update wave for all the Microsoft services like Window 8, Windows Phone 8, SkyDrive, Hotmail, and Windows Server, according to Mary Jo Foley's sources.
She also added that Microsoft is going to try to push Blue out to users far more quickly, possibly via the Windows Store for Windows 8 users. New versions of Internet Explorer, Mail, Calendar, Bing and other apps can be a part of Windows Blue.
Before these updates come to market, there will continue to be minor fixes, firmware updates and new features added to Windows 8, Windows RT, Windows Services and Windows Phone. On the phone side of the house, for example, the first minor update, codenamed Portico, already has made its way out to a number of Windows Phone users.
Charon at Ma-Config.com found a recent mention of Blue in a member of the Windows team's LinkedIn profile:
Source: Mary Jo Foley