While the invite doesn't refer to a specific device, it's a pretty safe bet to assume it's a new Nook Color, though it's unclear whether it will be called the Nook Color 2 or something else altogether. The new tablet will presumably have an upgraded processor and perhaps an upgraded screen and some additional design refinements.
The biggest question is how much the new tablet will cost. With the Kindle Fire on sale at $199 (it ships November 15), there's some pressure on B&N to come close to matching that price, though Amazon is allegedly losing money on each Fire it sells (our sources suggest the Fire currently costs around $220 to build). With that being the case, Barnes & Noble is more likely to come out with a faster, more powerful Nook Color that costs $249, though we wouldn't be surprised to see it at $299.
At the same time, the company may leave the original the Nook Color on the market and price it at $199.
Potentially, the one big advantage a new Nook Color would have over the Kindle Fire is more memory--or at least expandable memory. The Fire, which taps into Amazon's suite of audio, video, and Web services and features its new Silk Web browser and App Store for Android, has 8GB of internal memory (6GB usable) and no memory expansion slot.